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Configuring device mapper multipath
Configuring and managing the Device Mapper Multipath feature
Abstract
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Chapter 1. Overview of device mapper multipathing
DM Multipath provides:
- Redundancy
- DM Multipath can provide failover in an active/passive configuration. In an active/passive configuration, only a subset of the paths is used at any time for I/O. If any element of an I/O path such as the cable, switch, or controller fails, DM Multipath switches to an alternate path.
The number of paths is dependent on the setup. Usually, DM Multipath setups have 2, 4, or 8 paths to the storage, but this is a common setup and other numbers are possible for the paths.
- Improved Performance
- DM Multipath can be configured in an active/active mode, where I/O is spread over the paths in a round-robin fashion. In some configurations, DM Multipath can detect loading on the I/O paths and dynamically rebalance the load.
1.1. Active/Passive multipath configuration with one RAID device
In this configuration, there are two Host Bus Adapters (HBAs) on the server, two SAN switches, and two RAID controllers. Following are the possible failure in this configuration:
- HBA failure
- Fibre Channel cable failure
- SAN switch failure
- Array controller port failure
With DM Multipath configured, a failure at any of these points causes DM Multipath to switch to the alternate I/O path. The following image describes the configuration with two I/O paths from the server to a RAID device. Here, there is one I/O path that goes through hba1
, SAN1
, and cntrlr1
and a second I/O path that goes through hba2
, SAN2
, and cntrlr2
.
Figure 1.1. Active/Passive multipath configuration with one RAID device
![Active/Passive multipath configuration with one RAID device](https://access.redhat.com/webassets/avalon/d/Red_Hat_Enterprise_Linux-9-Configuring_device_mapper_multipath-en-US/images/546dd4418a38cd9b217853048dac5a96/active-passive-multipath-config-one-raid-device.png)
1.2. Active/Passive multipath configuration with two RAID devices
In this configuration, there are two HBAs on the server, two SAN switches, and two RAID devices with two RAID controllers each. With DM Multipath configured, a failure at any of the points of the I/O path to either of the RAID devices causes DM Multipath to switch to the alternate I/O path for that device. The following image describes the configuration with two I/O paths to each RAID device. Here, there are two I/O paths to each RAID device.
Figure 1.2. Active/Passive multipath configuration with two RAID device
![Active/Passive multipath configuration with two RAID device](https://access.redhat.com/webassets/avalon/d/Red_Hat_Enterprise_Linux-9-Configuring_device_mapper_multipath-en-US/images/3f9b7e1867c76aae8e9d69e98d13b521/active-passive-multipath-config-with-two-raid-devices.png)
1.3. Active/Active multipath configuration with one RAID device
In this configuration, there are two HBAs on the server, two SAN switches, and two RAID controllers. The following image describes the configuration with two I/O paths from the server to a storage device. Here, I/O can be spread among these two paths.
Figure 1.3. Active/Active multipath configuration with one RAID device
![Active/Active multipath configuration with one RAID device](https://access.redhat.com/webassets/avalon/d/Red_Hat_Enterprise_Linux-9-Configuring_device_mapper_multipath-en-US/images/546dd4418a38cd9b217853048dac5a96/active-passive-multipath-config-one-raid-device.png)
1.4. DM Multipath components
The following table describes the DM Multipath components.
Component | Description |
| Reroutes I/O and supports failover for paths and path groups. |
| Configures and enables device mapper multipathing. |
|
Lists and configures the multipath devices. It is also executed by |
|
Automatically creates and removes multipath devices and monitors paths; as paths fail and come back, it may update the multipath device. Allows interactive changes to multipath devices. Reload the service if there are any changes to the |
|
Creates device mapper devices for the partitions on a device. This command is automatically executed by |
|
Sets up |
1.5. The multipath command
The multipath
command is used to detect and combine multiple paths to devices. It provides a variety of options you can use to administer your multipathed devices.
The following table describes some options of the multipath
command that you may find useful.
Option | Description |
---|---|
|
Display the current multipath topology gathered from |
|
Display the current multipath topology gathered from |
| Remove the named multipath device. |
| Remove all unused multipath devices. |
|
Remove the |
|
Reset the |
| Force reload of the multipath device. |
1.6. Displaying multipath topology
To effectively monitor paths, troubleshoot multipath issues, or check whether the multipath configurations are set correctly, you can display the multipath topology.
Procedure
Display the multipath device topology:
# multipath -ll mpatha (3600d0230000000000e13954ed5f89300) dm-4 WINSYS,SF2372 size=233G features='1 queue_if_no_path' hwhandler='0' wp=rw `-+- policy='service-time 0' prio=1 status=active `- 6:0:0:0 sdf 8:80 active ready running
The output can be split into three parts. Each part displays information for the following group:
Multipath device information:
-
mpatha (3600d0230000000000e13954ed5f89300)
: alias (wwid if it’s different from the alias) -
dm-4
: dm device name -
WINSYS,SF2372
: vendor, product -
size=233G
: size -
features='1 queue_if_no_path'
: features -
hwhandler='0'
: hardware handler -
wp=rw
: write permissions
-
Path group information:
-
policy='service-time 0'
: scheduling policy -
prio=1
: path group priority -
status=active
: path group status
-
Path information:
-
6:0:0:0
: host:channel:id:lun -
sdf
: devnode -
8:80
: major:minor numbers -
active
: dm status -
ready
: path status running
: online statusFor more information about the dm, path and online status, see Path status.
-
Other multipath commands, which are used to list, create, or reload multipath devices, also display the device topology. However, some information might be unknown and shown as undef
in the output. This is normal behavior. Use the multipath -ll
command to view the correct state.
In certain cases, such as creating a multipath device, the multipath topology displays a parameter, which represents if any action was taken. For example, the following command output shows the create:
parameter to represent that a multipath device was created:
create: mpatha (3600d0230000000000e13954ed5f89300) undef WINSYS,SF2372
size=233G features='1 queue_if_no_path' hwhandler='0' wp=undef
`-+- policy='service-time 0' prio=1 status=undef
`- 6:0:0:0 sdf 8:80 undef ready running
1.7. Path status
The path status is updated periodically by the multipathd
daemon based on the polling interval defined in the /etc/multipath.conf
file. In terms of the kernel, the dm
status is similar to the path status. The dm
state will retain its current status until the path checker has completed.
- Path status
- ready, ghost
- The path is up and ready for I/O.
- faulty, shaky
- The path is down.
- i/o pending
- The checker is actively checking this path, and the state will be updated shortly.
- i/o timeout
-
The checker did not return
success
/failure
before the timeout period. This is treated the same asfaulty
. - removed
-
The path has been removed from the system, and will shortly be removed from the multipath device. This is treated the same as
faulty
. - wild
-
multipathd
was unable to run the path checker, because of an internal error or configuration issue. This is treated the same asfaulty
, except multipath will skip many actions on the path. - unchecked
-
The path checker has not run on this path, either because it has just been discovered, it does not have an assigned path checker, or the path checker encountered an error. This is treated the same as
wild
. - delayed
-
The path checker returns that the path is up, but multipath is delaying the reinstatement of the path because the path has recently failed multiple times and multipath has been configured to delay paths in this case. This is treated the same as
faulty
.
- Dm status
- Active
-
Maps to the
ready
andghost
path status. - Failed
-
Maps to all other path status, except
i/o pending
that does not have an equivalentdm
state.
- Online status
- Running
- The device is enabled.
- Offline
- The device has been disabled.
1.8. Additional resources
-
multipath(8)
andmultipathd(8)
man pages -
/etc/multipath.conf
file
Chapter 2. Multipath devices
DM Multipath provides a way of organizing the I/O paths logically, by creating a single multipath device on top of the underlying devices. Without DM Multipath, system treats each path from a server node to a storage controller as a separate device, even when the I/O path connects the same server node to the same storage controller.
2.1. Multipath device identifiers
When new devices are under the control of DM Multipath, these devices are created in the /dev/mapper/
and /dev/
directory.
Any devices of the form /dev/dm-X
are for internal use only and should never be used by the administrator directly.
The following describes multipath device names:
-
When the
user_friendly_names
configuration option is set tono
, the name of the multipath device is set to World Wide Identifier (WWID). By default, the name of a multipath device is set to its WWID. The device name would be/dev/mapper/WWID
. It is also created in the/dev/
directory, named as/dev/dm-X
. -
Alternately, you can set the
user_friendly_names
option toyes
in the/etc/multipath.conf
file. This sets thealias
in themultipath
section to a node-unique name of the formmpathN
. The device name would be/dev/mapper/mpathN
and/dev/dm-X
. But the device name is not guaranteed to be the same on all nodes using the multipath device. Similarly, if you set thealias
option in the/etc/multipath.conf
file, the name is not automatically consistent across all nodes in the cluster.
This should not cause any difficulties if you use LVM to create logical devices from the multipath device. To keep your multipath device names consistent in every node, Red Hat recommends disabling the user_friendly_names
option.
For example, a node with two HBAs attached to a storage controller with two ports by means of a single unzoned FC switch sees four devices: /dev/sda
, /dev/sdb
, /dev/sdc
, and /dev/sdd
. DM Multipath creates a single device with a unique WWID that reroutes I/O to those four underlying devices according to the multipath configuration.
In addition to the user_friendly_names
and alias
options, a multipath device also has other attributes. You can modify these attributes for a specific multipath device by creating an entry for that device in the multipaths
section of the /etc/multipath.conf
file.
Additional resources
-
multipath(8)
andmultipath.conf(8)
man pages -
/etc/multipath.conf
file - DM Multipath components
2.2. Multipath devices in logical volumes
After creating multipath devices, you can use the multipath device names as you would use a physical device name when creating an Logical volume manager (LVM) physical volume. For example, if /dev/mapper/mpatha
is the name of a multipath device, the pvcreate /dev/mapper/mpatha
command marks /dev/mapper/mpatha
as a physical volume.
You can use the resulting LVM physical device when you create an LVM volume group just as you would use any other LVM physical device.
To filter all the sd
devices in the /etc/lvm/lvm.conf
file, add the filter = [ "r/block/", "r/disk/", "r/sd./", "a/./" ]
filter in the devices
section of the file.
If you attempt to create an LVM physical volume on a whole device on which you have configured partitions, the pvcreate
command fails. The Anaconda and Kickstart installation programs create empty partition tables if you do not specify otherwise for every block device. If you want to use the whole device instead of creating a partition, remove the existing partitions from the device. You can remove existing partitions with the kpartx -d
device command and the fdisk
utility. If your system has block devices that are greater than 2Tb, use the parted
utility to remove partitions.
When you create an LVM logical volume that uses active/passive
multipath arrays as the underlying physical devices, you can optionally include filters in the /etc/lvm/lvm.conf
file to exclude the disks that underline the multipath devices. This is because if the array automatically changes the active path to the passive path when it receives I/O, multipath will failover and failback whenever LVM scans the passive path, if these devices are not filtered.
The kernel changes the active/passive state by automatically detecting the correct hardware handler to use. For active/passive paths that require intervention to change their state, multipath automatically uses this hardware handler to do so as necessary. If the kernel does not automatically detect the correct hardware handler to use, you can configure which hardware handler to use in the multipath.conf file with the "hardware_handler" option. For active/passive
arrays that require a command to make the passive path active, LVM prints a warning message when this occurs.
Depending on your configuration, LVM may print any of the following messages:
LUN not ready:
end_request: I/O error, dev sdc, sector 0 sd 0:0:0:3: Device not ready: <6>: Current: sense key: Not Ready Add. Sense: Logical unit not ready, manual intervention required
Read failed:
/dev/sde: read failed after 0 of 4096 at 0: Input/output error
The following are the reasons for the mentioned errors:
- Multipath is not set up on storage devices that are providing active/passive paths to a machine.
- Paths are accessed directly, instead of through the multipath device.
Additional resources
-
lvm.conf
man page - DM Multipath components
Chapter 3. Configuring DM Multipath
You can set up DM Multipath with the mpathconf
utility. This utility creates or edits the /etc/multipath.conf
multipath configuration file based on the following scenarios:
-
If the
/etc/multipath.conf
file already exists, thempathconf
utility will edit it. -
If the
/etc/multipath.conf
file does not exist, thempathconf
utility will create the/etc/multipath.conf
file from scratch.
3.1. Checking for the device-mapper-multipath package
Before setting up DM Multipath on your system, ensure that your system is up-to-date and includes the device-mapper-multipath
package.
Procedure
Check if your system includes the
device-mapper-multipath
package:# rpm -q device-mapper-multipath device-mapper-multipath-current-package-version
If your system does not include the package, it prints the following:
package device-mapper-multipath is not installed
If your system does not include the package, install it by running the following command:
# dnf install device-mapper-multipath
3.2. Setting up basic failover configuration with DM Multipath
You can set up DM Multipath for a basic failover configuration and edit the /etc/multipath.conf
file before starting the multipathd daemon.
Prerequisites
- Administrative access.
Procedure
Enable and initialize the multipath configuration file:
# mpathconf --enable
Optional: Edit the
/etc/multipath.conf
file.Most default settings are already configured, including
path_grouping_policy
which is set tofailover
.Optional: The default naming format of multipath devices is set to
/dev/mapper/mpathn
format. If you prefer a different naming format:Configure DM Multipath to use the multipath device WWID as its name, instead of the mpath_n_ user-friendly naming scheme:
# mpathconf --enable --user_friendly_names n
Reload the configuration of the DM Multipath daemon:
# systemctl reload multipathd.service
Start the DM Multipath daemon:
# systemctl start multipathd.service
Verification
Confirm that the DM Multipath daemon is running without issues:
# systemctl status multipathd.service
Verify the naming format of multipath devices:
# ls /dev/mapper/
3.3. Ignoring local disks when generating multipath devices
Some machines have local SCSI cards for their internal disks and DM Multipath is not recommended for these devices. If you set the find_multipaths
configuration parameter to yes
, you do not have to disable multipathing on these devices.
If you do not set the find_multipaths
configuration parameter to yes
, you can use the following procedure to modify the DM Multipath configuration file to ignore the local disks when configuring multipath.
Procedure
Identify the internal disk using any known parameters such as the device’s model, path or vendor, and determine its WWID by using any one of the following options:
Display existing multipath devices:
# multipath -v2 -l mpatha (WDC_WD800JD-75MSA3_WD-WMAM9FU71040) dm-2 ATA,WDC WD800JD-75MS size=33 GB features="0" hwhandler="0" wp=rw `-+- policy='round-robin 0' prio=0 status=active |- 0:0:0:0 sda 8:0 active undef running
Display additional multipath devices that DM Multipath could create:
# multipath -v2 -d : mpatha (WDC_WD800JD-75MSA3_WD-WMAM9FU71040) dm-2 ATA,WDC WD800JD-75MS size=33 GB features="0" hwhandler="0" wp=undef `-+- policy='round-robin 0' prio=1 status=undef |- 0:0:0:0 sda 8:0 undef ready running
Display device information:
# multipathd show paths raw format "%d %w" | grep sda sda WDC_WD800JD-75MSA3_WD-WMAM9FU71040
In this example,
/dev/sda
is the internal disk and its WWID isWDC_WD800JD-75MSA3_WD-WMAM9FU71040
.
Edit the
blacklist
section of the/etc/multipath.conf
file to ignore this device, using its WWID attribute:blacklist { wwid WDC_WD800JD-75MSA3_WD-WMAM9FU71040 }
WarningAlthough you could identify the device using its
devnode
parameter, such assda
, it would not be a safe procedure, because/dev/sda
is not guaranteed to refer to the same device on reboot.Check for any configuration errors in the
/etc/multipath.conf
file:# multipath -t > /dev/null
To see the full report, do not discard the command output:
# multipath -t
-
If the disk is included in
initramfs
remake the initramfs. For more information see Configuring multipathing in initramfs. Reload the
/etc/multipath.conf
file by reconfiguring themultipathd
daemon:# systemctl reload multipathd
Multipath devices on top of local disks cannot be removed when in use. To ignore such device, stop all users of the device. For example, by unmounting any filesystem on top of it and deactivating any logical volumes using it. If this is not possible, you can reboot the system to remove the multipath device.
Verification
Verify that the internal disk is ignored and it is not displayed in the multipath output:
List the multipathed devices:
# multipath -v2 -l
List the additional devices that DM Multipath could create:
# multipath -v2 -d
Additional resources
-
multipath.conf(5)
man page
3.4. Configuring additional storage with DM Multipath
By default, DM Multipath includes built-in configurations for the most common storage arrays, which support DM Multipath. If your storage array does not already have a configuration, you can add one by editting the /etc/multipath.conf
file.
- NOTE
- Add additional storage devices during the initial configuration to align the setup with your anticipated needs. DM Multipath enables adding devices later for scalability or upgrades, but this approach may require adjusting configurations to ensuring compatibility.
Prerequisites
- Administrative access.
Procedure
View the default configuration value and supported devices:
# multipathd show config
Edit the
/etc/multipath.conf
file to set up your multipath configuration.Example 3.1. DM Multipath Configuration for HP OPEN-V Storage Device
# Set default configurations for all devices managed by DM Multipath defaults { # Enable user-friendly names for devices user_friendly_names yes } devices { # Define configuration for HP OPEN-V storage device { vendor "HP" pproduct "OPEN-V" no_path_retry 18 } }
- Save your changes and close the editor.
Update the multipath device list by scanning for new devices:
# multipath -r
Verification
Confirm that the multipath devices are recognized correctly:
# multipath -ll
3.5. Configuring multipathing in initramfs
Setting up multipathing in the initramfs
file system is essential for seamless storage functionality, particularly in scenarios requiring redundancy and load balancing. This setup guarantees that multipath devices are available early in the boot process, which is crucial for maintaining the integrity of the storage setup and preventing potential issues.
Prerequisites
- Administrative access.
- Configured DM multipath on your system.
Procedure
Rebuild the
initramfs
file system with the multipath configuration files:# dracut --force --add multipath
- NOTE
-
When using multipath in the
initramfs
and modifying its configuration files, remember to rebuild theinitramfs
for the changes to tale effect. If your root device employs multipath, thedracut
command will automatically include the multipath module in theinitramfs
.
Optional: If multipath in the
initramfs
is no longer necessary:Remove the multipath configuration file:
# rm /etc/dracut.conf.d/multipath.conf
Rebuild the
initramfs
with the added multipath configuration:# dracut --force --omit multipath
Verification
Check if multipath-related files and configurations are present:
# lsinitrd /path/to/initramfs.img -m | grep multipath
- NOTE
- While verefication steps provided can give you an indication of success, a final test boot-up is recommended to ensure that the configuration works as expected.
After the reboot, confirm that the multipath devices are recognized correctly:
# multipath -ll
Chapter 4. Enabling multipathing on NVMe devices
You can multipath Non-volatile Memory Express™ (NVMe™) devices that are connected to your system over a fabric transport, such as Fibre Channel (FC). You can select between multiple multipathing solutions.
4.1. Native NVMe multipathing and DM Multipath
Non-volatile Memory Express™ (NVMe™) devices support a native multipathing functionality. When configuring multipathing on NVMe, you can select between the standard DM Multipath framework and the native NVMe multipathing.
Both DM Multipath and native NVMe multipathing support the Asymmetric Namespace Access (ANA) multipathing scheme of NVMe devices. ANA identifies optimized paths between the controller and the host, and improves performance.
When native NVMe multipathing is enabled, it applies globally to all NVMe devices. It can provide higher performance, but does not contain all of the functionality that DM Multipath provides. For example, native NVMe multipathing supports only the numa
and round-robin
path selection methods.
By default, NVMe multipathing is enabled in Red Hat Enterprise Linux 9 and is the recommended multipathing solution.
4.2. Enabling DM Multipath on NVMe devices
The default kernel setting for the nvme_core.multipath
option is set to Y
, which means that the native Non-volatile Memory Express™ (NVMe™) multipathing is enabled. You can enable DM Multipath on connected NVMe devices by disabling native NVMe multipathing.
Prerequisites
- The NVMe devices are connected to your system. For more information, see Overview of NVMe over fabric devices.
Procedure
Check if the native NVMe multipathing is enabled:
# cat /sys/module/nvme_core/parameters/multipath
The command displays one of the following:
N
- Native NVMe multipathing is disabled.
Y
- Native NVMe multipathing is enabled.
If the native NVMe multipathing is enabled, disable it by using one of the following methods:
Using a kernel option:
Add the
nvme_core.multipath=N
option to the command line:# grubby --update-kernel=ALL --args="nvme_core.multipath=N"
On the 64-bit IBM Z architecture, update the boot menu:
# zipl
- Reboot the system.
Using a kernel module configuration file:
Create the
/etc/modprobe.d/nvme_core.conf
configuration file with the following content:options nvme_core multipath=N
Back up the
initramfs
file:# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).bak.$(date +%m%d-%H%M%S).img
Rebuild the
initramfs
:# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).bak.$(date +%m-%d-%H%M%S).img # dracut --force --verbose
- Reboot the system.
Enable DM Multipath:
# systemctl enable --now multipathd.service
Distribute I/O on all available paths. Add the following content in the
/etc/multipath.conf
file:devices { device { vendor "NVME" product ".*" path_grouping_policy group_by_prio } }
NoteThe
/sys/class/nvme-subsystem/nvme-subsys0/iopolicy
configuration file has no effect on the I/O distribution when DM Multipath manages the NVMe devices.Reload the
multipathd
service to apply the configuration changes:# multipath -r
Verification
Verify if the native NVMe multipathing is disabled:
# cat /sys/module/nvme_core/parameters/multipath N
Verify if DM multipath recognizes the nvme devices:
# multipath -l eui.00007a8962ab241100a0980000d851c8 dm-6 NVME,NetApp E-Series size=20G features='0' hwhandler='0' wp=rw `-+- policy='service-time 0' prio=0 status=active |- 0:10:2:2 nvme0n2 259:3 active undef running `-+- policy='service-time 0' prio=0 status=enabled |- 4:11:2:2 nvme4n2 259:28 active undef running `-+- policy='service-time 0' prio=0 status=enabled |- 5:32778:2:2 nvme5n2 259:38 active undef running `-+- policy='service-time 0' prio=0 status=enabled |- 6:32779:2:2 nvme6n2 259:44 active undef running
Additional resources
4.3. Enabling native NVMe multipathing
If native NVMe multipathing is disabled, you can enable it using the following solution.
Prerequisites
- The NVMe devices are connected to your system. For more information, see Overview of NVMe over fabric devices.
Procedure
Check if native NVMe multipathing is enabled in the kernel:
# cat /sys/module/nvme_core/parameters/multipath
The command displays one of the following:
N
- Native NVMe multipathing is disabled.
Y
- Native NVMe multipathing is enabled.
If native NVMe multipathing is disabled, enable it by using one of the following methods:
Using a kernel option:
Remove the
nvme_core.multipath=N
option from the kernel command line:# grubby --update-kernel=ALL --remove-args="nvme_core.multipath=N"
On the 64-bit IBM Z architecture, update the boot menu:
# zipl
- Reboot the system.
Using a kernel module configuration file:
Remove the
/etc/modprobe.d/nvme_core.conf
configuration file:# rm /etc/modprobe.d/nvme_core.conf
Back up the
initramfs
file:# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).bak.$(date +%m-%d-%H%M%S).img
Rebuild the
initramfs
:# dracut --force --verbose
- Reboot the system.
Optional: On the running system, change the I/O policy on NVMe devices to distribute the I/O on all available paths:
# echo "round-robin" > /sys/class/nvme-subsystem/nvme-subsys0/iopolicy
Optional: Set the I/O policy persistently using
udev
rules. Create the/etc/udev/rules.d/71-nvme-io-policy.rules
file with the following content:ACTION=="add|change", SUBSYSTEM=="nvme-subsystem", ATTR{iopolicy}="round-robin"
Verification
Verify if your system recognizes the NVMe devices. The following example assumes you have a connected NVMe over fabrics storage subsystem with two NVMe namespaces:
# nvme list Node SN Model Namespace Usage Format FW Rev ---------------- -------------------- ---------------------------------------- --------- -------------------------- ---------------- -------- /dev/nvme0n1 a34c4f3a0d6f5cec Linux 1 250.06 GB / 250.06 GB 512 B + 0 B 4.18.0-2 /dev/nvme0n2 a34c4f3a0d6f5cec Linux 2 250.06 GB / 250.06 GB 512 B + 0 B 4.18.0-2
List all connected NVMe subsystems:
# nvme list-subsys nvme-subsys0 - NQN=testnqn \ +- nvme0 fc traddr=nn-0x20000090fadd597a:pn-0x10000090fadd597a host_traddr=nn-0x20000090fac7e1dd:pn-0x10000090fac7e1dd live +- nvme1 fc traddr=nn-0x20000090fadd5979:pn-0x10000090fadd5979 host_traddr=nn-0x20000090fac7e1dd:pn-0x10000090fac7e1dd live +- nvme2 fc traddr=nn-0x20000090fadd5979:pn-0x10000090fadd5979 host_traddr=nn-0x20000090fac7e1de:pn-0x10000090fac7e1de live +- nvme3 fc traddr=nn-0x20000090fadd597a:pn-0x10000090fadd597a host_traddr=nn-0x20000090fac7e1de:pn-0x10000090fac7e1de live
Check the active transport type. For example,
nvme0 fc
indicates that the device is connected over the Fibre Channel transport, andnvme tcp
indicates that the device is connected over TCP.If you edited the kernel options, verify if native NVMe multipathing is enabled on the kernel command line:
# cat /proc/cmdline BOOT_IMAGE=[...] nvme_core.multipath=Y
If you changed the I/O policy, verify if
round-robin
is the active I/O policy on NVMe devices:# cat /sys/class/nvme-subsystem/nvme-subsys0/iopolicy round-robin
Additional resources
Chapter 5. Modifying the DM Multipath configuration file
By default, DM Multipath provides configuration values for the most common uses of multipathing. In addition, DM Multipath includes support for the most common storage arrays that themselves support DM Multipath. You can override the default configuration values for DM Multipath by editing the /etc/multipath.conf
configuration file. If necessary, you can also add an unsupported by default storage array to the configuration file.
For information about the default configuration values, including supported devices, run either of the following commands:
# multipathd show config # multipath -t
If you run multipath from the initramfs
file system and you make any changes to the multipath configuration files, you must rebuild the initramfs
file system for the changes to take effect
In the multipath configuration file, you need to specify only the sections that you need for your configuration, or that you need to change from the default values. If there are sections of the file that are not relevant to your environment or for which you do not need to override the default values, you can leave them commented out, as they are in the initial file.
The configuration file allows regular expression description syntax.
5.1. Configuration file overview
The multipath configuration file is divided into the following sections:
- blacklist
- Listing of specific devices that will not be considered for multipath.
- blacklist_exceptions
-
Listing of multipath devices that would otherwise be ignored according to the parameters of the
blacklist
section. - defaults
- General default settings for DM Multipath.
- multipaths
-
Settings for the characteristics of individual multipath devices. These values overwrite what is specified in the
overrides
,devices
, anddefaults
sections of the configuration file. - devices
-
Settings for the individual storage controllers. These values overwrite what is specified in the
defaults
section of the configuration file. If you are using a storage array that is not supported by default, you may need to create adevices
subsection for your array. - overrides
-
Settings that are applied to all devices. These values overwrite what is specified in the
devices
anddefaults
sections of the configuration file.
When the system determines the attributes of a multipath device, it checks the settings of the separate sections from the multipath.conf
file in the following order:
-
multipaths
section -
overrides
section -
devices
section -
defaults
section
5.2. Configuration file defaults
The /etc/multipath.conf
configuration file contains a defaults
section. This section includes the default configuration of Device Mapper (DM) Multipath. The default values might differ based on your initial device settings.
The following are the ways to view the default configurations:
If you install your machine on a multipath device, the default multipath configuration applies automatically. The default configuration includes the following:
-
For a complete list of the default configuration values, execute either
multipath -t
ormultipathd show config
command. -
For a list of configuration options with descriptions, see the
multipath.conf
man page.
-
For a complete list of the default configuration values, execute either
-
If you did not set up multipathing during installation, execute the
mpathconf --enable
command to get the default configuration.
The following table describes the attributes, set in the defaults
section of the multipath.conf
configuration file. Attributes specified in the multipaths
section have higher priority over values in the devices
section. Attributes specified in the devices
section have higher priority over the default values. Use the overrides
section to set attribute values for all device types, even if those device types have a builtin configuration entry in the devices
section. The overrides
section has no mandatory attributes. However, any attribute set in this section takes precedence over values in the devices
or defaults
sections.
Attribute | Description |
---|---|
|
Specifies the interval between two path checks in seconds. For properly functioning paths, the interval between checks gradually increases to |
| Specifies the maximum length of the interval between two path checks in seconds. |
The default value is | |
| Defines the mode for setting up multipath devices. Available values include: |
| |
| |
| |
| |
| |
The default value is | |
|
This represents the timeout in seconds, to wait for additional paths after detecting the first one, if |
Positive value: If set with a positive value, the timeout applies for all non-blacklisted devices. | |
Negative value: If set with a negative value, the timeout applies only to known devices that have an entry in the multipath hardware table, either in the built-in table, or in a | |
| |
The default value for known hardware is | |
|
Set the timeout of |
For systems with a large number of devices, | |
The default value is | |
|
Enable reassigning of device-mapper maps. With this option, the |
|
The default verbosity value is |
| Specifies the default algorithm to use in determining what path to use for the next I/O operation. Possible values include: |
| |
| |
| |
The default value is | |
| Specifies the default path grouping policy to apply to unspecified multipaths. Possible values include: |
| |
| |
| |
| |
| |
The default value is | |
|
Set this option to activate merging |
The value of this option is a space separated list of records like | |
If you configure this option and it matches the device node name of a device, it overrides any other configured methods for determining the WWID for this device. | |
You can enable | |
The default is | |
|
Specifies the default function to call to obtain a path priority value. For example, the ALUA bits in SPC-3 provide an exploitable |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
The default value depends on the | |
|
Arguments to pass to the |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
The default value is | |
| The default extra features of multipath devices, using the format: "number_of_features_plus_arguments feature1 …". |
Possible values for | |
| |
| |
| |
| |
By default, the value is unset. | |
| Specifies the default method to determine the state of the paths. Possible values include: |
| |
| |
| |
| |
| |
| |
| |
| |
The default value is | |
|
This attribute represents the |
The default value is | |
| Manages path group failback. Possible values include: |
| |
| |
| |
A numeric value greater than zero, specifies deferred failback, and is expressed in seconds. | |
The default value is | |
|
Specifies the number of I/O requests to route to a path before switching to the next path in the current path group. This setting is only for systems running kernels older than 2.6.31. Newer systems should use |
|
Specifies the number of I/O requests to route to a path, before switching to the next path in the current path group. Uses a request-based device-mapper-multipath. This setting can be used on systems running current kernels. On systems running kernels older than 2.6.31, use |
| A numeric value for this attribute specifies the number of times that the path checker must fail for all paths in a multipath device, before disabling queuing. |
A value of | |
A value of | |
The default value is | |
| Possible values include: |
| |
| |
The default value is | |
|
If set to |
|
If set to |
|
Sets the maximum number of open file descriptors that can be opened by multipath and the |
|
The timeout to use for prioritizers and path checkers that issue SCSI commands with an explicit timeout, in seconds. The |
|
The number of seconds the SCSI layer waits after a problem is detected on an FC remote port, before failing I/O to devices on that remote port. This value must be smaller than the value of |
| The number of seconds the SCSI layer waits after a problem is detected on an FC remote port, before removing it from the system. Setting this to infinity will set this to 2147483647 seconds, or 68 years. The OS determines the default value. |
|
Specifies the maximum number of seconds the SCSI layer spends performing error handling, when SCSI devices fail. After this timeout, the scsi layer performs a full HBA reset. Setting this is necessary in cases where the |
The default value is | |
|
If this is set to |
If | |
The default value is | |
|
Specifies the |
The default value is device dependent: | |
|
If set to |
The default value is | |
|
If set to |
The default value is | |
|
Use the |
The default value of | |
|
This attribute controls the number of seconds the |
The default value is | |
|
If set to |
|
If you set all three of these attributes to integers greater than zero, they enable the |
See the Shaky paths detection section of the | |
The default value is | |
|
If |
If a path fails twice within the value set in the | |
See the Shaky paths detection section of the | |
The default value is | |
| Possible values include: |
| |
| |
| |
The | |
See the Shaky paths detection section of the | |
The default value is | |
|
If set to |
|
If set to |
|
Using this option, you can set the |
|
This attribute sets the number of seconds that multipath waits after creating a device with only ghost paths, before marking it ready for use in |
Setting this to | |
The default value is | |
| This attribute enables or disables foreign libraries. |
The value is a regular expression. Foreign libraries are loaded if their name matches the expression. | |
By default, no foreign libraries are enabled. Use | |
|
If set to |
This option only works for SCSI devices with configuration to use the default | |
The default value is | |
|
This option sets the number of times multipath retries removing a device that is in use. Between each attempt, multipath becomes inactive for 1 second. The default value is |
|
If set to |
The default value is | |
|
The |
This parameter can also be set to | |
|
If this option is set to |
|
Controls when the |
| |
| |
|
Additional resources
-
multipath.conf(5)
man page
5.3. Configuration file multipaths section
Set attributes of individual multipath devices by using the multipaths
section of the multipath.conf
configuration file. Device Mapper (DM) Multipath uses these attributes to override all other configuration settings, including those from the overrides
section. Refer to Configuration file overrides section for a list of attributes from the overrides
section.
The multipaths
section recognizes only the multipath
subsection as an attribute. The following table shows the attributes that you can set in the multipath
subsection, for each specific multipath device. These attributes apply only to one specified multipath. If several multipath
subsections match a specific device World Wide Identifier (WWID), the contents of those subsections merge. The settings from latest entries have priority over any previous versions.
Attribute | Description |
---|---|
|
Specifies the WWID of the multipath device, to which the multipath attributes apply. This parameter is mandatory for this section of the |
|
Specifies the symbolic name for the multipath device, to which the multipath attributes apply. If you are using |
The attributes in the following list are optional. If you do not set them, default values from the overrides
, devices
, or defaults
sections apply. Refer to Configuration file defaults for a full description of these attributes.
-
path_grouping_policy
-
path_selector
-
prio
-
prio_args
-
failback
-
no_path_retry
-
rr_min_io
-
rr_min_io_rq
-
flush_on_last_del
-
features
-
reservation_key
-
user_friendly_names
-
deferred_remove
-
san_path_err_threshold
-
san_path_err_forget_rate
-
san_path_err_recovery_time
-
marginal_path_err_sample_time
-
marginal_path_err_rate_threshold
-
marginal_path_err_recheck_gap_time
-
marginal_path_double_failed_time
-
delay_watch_checks
-
delay_wait_checks
-
skip_kpartx
-
max_sectors_kb
-
ghost_delay
The following example shows multipath attributes specified in the configuration file for two specific multipath devices. The first device has a WWID of 3600508b4000156d70001200000b0000
and a symbolic name of yellow
.
The second multipath device in the example has a WWID of 1DEC_321816758474
and a symbolic name of red
.
Example 5.1. Multipath attributes specification
multipaths {
multipath {
wwid 3600508b4000156d70001200000b0000
alias yellow
path_grouping_policy multibus
path_selector "round-robin 0"
failback manual
no_path_retry 5
}
multipath {
wwid 1DEC_321816758474
alias red
}
}
Additional resources
-
multipath.conf(5)
man page - Configuration file defaults
- Configuration file overrides section
5.4. Configuration file devices section
Use the devices
section of the multipath.conf
configuration file to define settings for individual storage controller types. Values set in this section overwrite specified values in the defaults
section.
The system identifies the storage controller types by the vendor
, product
, and revision
keywords. These keywords are regular expressions and must match the sysfs
information about the specific device.
The devices
section recognizes only the device
subsection as an attribute. If there are multiple keyword matches for a device, the attributes of all matching entries apply to it. If an attribute is specified in several matching device
subsections, later versions of entries have priority over any previous entries.
Configuration attributes in the latest version of the device
subsections override attributes in any previous devices
subsections and from the defaults
section.
The following table shows the attributes that you can set in the device
subsection.
Attribute | Description |
---|---|
| Specifies the regular expression to match the device vendor name. This is a mandatory attribute. |
| Specifies the regular expression to match the device product name. This is a mandatory attribute. |
| Specifies the regular expression to match the device product revision. If the revision attribute is missing, all device revisions match. |
|
Multipath uses this attribute to create a device |
| Shows the vendor specific Vital Product Data (VPD) page information, using the VPD page abbreviation. |
The | |
| Specifies the hardware handler to use for a particular device type. All possible values are hardware dependent and include: |
| |
| |
| |
| |
| |
The default value is |
Linux kernels, versions 4.3 and newer, automatically attach a device handler to known devices. This includes all devices supporting SCSI-3 ALUA). The kernel does not enable changing the handler later on. Setting the hardware_handler attribute for such devices on these kernels takes no effect.
The attributes in the following list are optional. If you do not set them, the default values from the defaults
sections apply. Refer to Configuration file defaults for a full description of these attributes.
-
path_grouping_policy
-
uid_attribute
-
getuid_callout
-
path_selector
-
path_checker
-
prio
-
prio_args
-
failback
-
alias_prefix
-
no_path_retry
-
rr_min_io
-
rr_min_io_rq
-
flush_on_last_del
-
features
-
reservation_key
-
user_friendly_names
-
deferred_remove
-
san_path_err_threshold
-
san_path_err_forget_rate
-
san_path_err_recovery_time
-
marginal_path_err_sample_time
-
marginal_path_err_rate_threshold
-
marginal_path_err_recheck_gap_time
-
marginal_path_double_failed_time
-
delay_watch_checks
-
delay_wait_checks
-
skip_kpartx
-
max_sectors_kb
-
ghost_delay
-
all_tg_pt
Additional resources
-
multipath.conf(5)
man page - Configuration file defaults
5.5. Configuration file overrides section
The overrides
section recognizes the optional protocol
subsection, and can contain multiple protocol
subsections. The system matches path devices against the protocol
subsection, using the mandatory type
attribute. Attributes in a matching protocol
subsection have priority over attributes in the rest of the overrides
section. If there are multiple matching protocol
subsections, later entries have higher priority.
The attributes in the following list are optional. If you do not set them, default values from the devices
or defaults
sections apply.
-
path_grouping_policy
-
uid_attribute
-
getuid_callout
-
path_selector
-
path_checker
-
alias_prefix
-
features
-
prio
-
prio_args
-
failback
-
no_path_retry
-
rr_min_io
-
rr_min_io_rq
-
flush_on_last_del
-
fast_io_fail_tmo
-
dev_loss_tmo
-
eh_deadline
-
user_friendly_names
-
retain_attached_hw_handler
-
detect_prio
-
detect_checker
-
deferred_remove
-
san_path_err_threshold
-
san_path_err_forget_rate
-
san_path_err_recovery_time
-
marginal_path_err_sample_time
-
marginal_path_err_rate_threshold
-
marginal_path_err_recheck_gap_time
-
marginal_path_double_failed_time
-
delay_watch_checks
-
delay_wait_checks
-
skip_kpartx
-
max_sectors_kb
-
ghost_delay
-
all_tg_pt
The protocol
subsection recognizes the following mandatory attribute:
Attribute | Description |
---|---|
| Specifies the protocol string of the path device. Possible values include: |
| |
This attribute is not a regular expression. The path device protocol string must match exactly. |
The attributes in the following list are optional for the protocol
subsection. If you do not set them, default values from the overrides
, devices
or defaults
sections apply.
-
fast_io_fail_tmo
-
dev_loss_tmo
-
eh_deadline
Additional resources
-
multipath.conf(5)
man page - Configuration file defaults
5.6. DM Multipath overrides of the device timeout
The recovery_tmo
sysfs
option controls the timeout for a particular iSCSI device. The following options globally override the recovery_tmo
values:
-
The
replacement_timeout
configuration option globally overrides therecovery_tmo
value for all iSCSI devices. For all iSCSI devices that are managed by DM Multipath, the
fast_io_fail_tmo
option in DM Multipath globally overrides therecovery_tmo
value.The
fast_io_fail_tmo
option in DM Multipath also overrides thefast_io_fail_tmo
option in Fibre Channel devices.
The DM Multipath fast_io_fail_tmo
option takes precedence over replacement_timeout
. Red Hat does not recommend using replacement_timeout
to override recovery_tmo
in devices managed by DM Multipath because DM Multipath always resets recovery_tmo
, when the multipathd
service reloads.
5.7. Modifying multipath configuration file defaults
The /etc/multipath.conf
configuration file includes a defaults
section that sets the user_friendly_names
parameter to yes
, as follows.
defaults { user_friendly_names yes }
This overwrites the default value of the user_friendly_names
parameter. The default values that are set in the defaults section on the multipath.conf file
, are used by DM Multipath unless they are overwritten by the attributes specified in the devices, multipath, or overrides sections of the multipath.conf
file.
Procedure
View the
/etc/multipath.conf
configuration file, which includes a template of configuration defaults:#defaults { # polling_interval 10 # path_selector "round-robin 0" # path_grouping_policy multibus # uid_attribute ID_SERIAL # prio alua # path_checker readsector0 # rr_min_io 100 # max_fds 8192 # rr_weight priorities # failback immediate # no_path_retry fail # user_friendly_names yes #}
Overwrite the default value for any of the configuration parameters. You can copy the relevant line from this template into the
defaults
section and uncomment it.For example, to overwrite the
path_grouping_policy
parameter tomultibus
instead of the default value offailover
, copy the appropriate line from the template to the initial defaults section of the configuration file, and uncomment it, as follows:defaults { user_friendly_names yes path_grouping_policy multibus }
Validate the
/etc/multipath.conf
file after modifying the multipath configuration file by running one of the following commands:To display any configuration errors, run:
# multipath -t > /dev/null
To display the new configuration with the changes added, run:
# multipath -t
Reload the
/etc/multipath.conf
file and reconfigure themultipathd
daemon for changes to take effect:# service multipathd reload
Additional resources
-
multipath.conf(5)
andmultipathd(8)
man pages
5.8. Modifying multipath settings for specific devices
In the multipaths
section of the multipath.conf
configuration file, you can add configurations that are specific to an individual multipath device, referenced by the mandatory WWID parameter.
These defaults are used by DM Multipath and override attributes set in the overrides
, defaults
, and devices
sections of the multipath.conf
file. There can be any number of multipath subsections in the multipaths
section.
Procedure
Modify the
multipaths
section for specific multipath device. The following example shows multipath attributes specified in the configuration file for two specific multipath devices:-
The first device has a WWID of
3600508b4000156d70001200000b0000
and a symbolic name ofyellow
. -
The second multipath device in the example has a WWID of
1DEC_321816758474
and a symbolic name ofred
.
In this example, the
rr_weight
attribute is set topriorities
.multipaths { multipath { wwid 3600508b4000156d70001200000b0000 alias yellow path_grouping_policy multibus path_selector "round-robin 0" failback manual rr_weight priorities no_path_retry 5 } multipath { wwid 1DEC_321816758474 alias red rr_weight priorities } }
-
The first device has a WWID of
Validate the
/etc/multipath.conf
file after modifying the multipath configuration file by running one of the following commands:To display any configuration errors, run:
# multipath -t > /dev/null
To display the new configuration with the changes added, run:
# multipath -t
Reload the
/etc/multipath.conf
file and reconfigure themultipathd
daemon for changes to take effect:# service multipathd reload
Additional resources
-
multipath.conf(5)
man page
5.9. Modifying the multipath configuration for specific devices with protocol
You can configure multipath device paths, based on their transport protocol. By using the protocol
subsection of the overrides
section in the /etc/multipath.conf
file, you can override the multipath configuration settings on certain paths. This enables access to multipath devices over multiple transport protocols, like Fiber Channel (FC) or Internet Small Computer Systems Interface (iSCSI).
Options set in the protocol
subsection override values in the overrides
, devices
and defaults
sections. These options apply only to devices using a transport protocol which matches the type
parameter of the subsection.
Prerequisites
- You have configured Device Mapper (DM) multipath in your system.
- You have multipath devices where not all paths use the same transport protocol.
Procedure
View the specific path protocol by running the following:
# multipathd show paths format "%d %P" dev protocol sda scsi:ata sdb scsi:fcp sdc scsi:fcp
Edit the
overrides
section of the/etc/multipath.conf
file, by addingprotocol
subsections for each multipath type.Settings for path devices, which use the
scsi:fcp
protocol:overrides { dev_loss_tmo 60 fast_io_fail_tmo 8 protocol { type "scsi:fcp" dev_loss_tmo 70 fast_io_fail_tmo 10 eh_deadline 360 } }
Settings for path devices, which use the
scsi:iscsi
protocol:overrides { dev_loss_tmo 60 fast_io_fail_tmo 8 protocol { type "scsi:iscsi" dev_loss_tmo 60 fast_io_fail_tmo 120 } }
Settings for path devices, which use all other protocols:
overrides { dev_loss_tmo 60 fast_io_fail_tmo 8 protocol { type "<type of protocol>" dev_loss_tmo 60 fast_io_fail_tmo 8 } }
The overrides
section can include multiple protocol
subsections.
The protocol
subsection must include a type
parameter. The configuration of all paths with a matching type
parameter is then updated with the rest of the parameters listed in the protocol
subsection.
Additional resources
-
multipath.conf(5)
man page
5.10. Modifying multipath settings for storage controllers
The devices
section of the multipath.conf
configuration file sets attributes for individual storage devices. These attributes are used by DM Multipath unless they are overwritten by the attributes specified in the multipaths
or overrides
sections of the multipath.conf
file for paths that contain the device. These attributes override the attributes set in the defaults
section of the multipath.conf
file.
Procedure
View the information about the default configuration value, including supported devices:
# multipathd show config # multipath -t
Many devices that support multipathing are included by default in a multipath configuration.
-
Optional: If you need to modify the default configuration values, you can overwrite the default values by including an entry in the configuration file for the device that overwrites those values. You can copy the device configuration defaults for the device that the
multipathd show config
command displays and override the values that you want to change. Add a device that is not configured automatically by default to the
devices
section of the configuration file by setting thevendor
andproduct
parameters. Find these values by opening the/sys/block/device_name/device/vendor
and/sys/block/device_name/device/model
files where device_name is the device to be multipathed, as mentioned in the following example:# cat /sys/block/sda/device/vendor WINSYS # cat /sys/block/sda/device/model SF2372
Optional: Specify the additional parameters depending on your specific device:
active/active
device-
Usually there is no need to set additional parameters in this case. If required, you might set
path_grouping_policy
tomultibus
. Other parameters you may need to set areno_path_retry
andrr_min_io
. active/passive
device-
If it automatically switches paths with I/O to the passive path, you need to change the checker function to one that does not send I/O to the path to test if it is working, otherwise, your device will keep failing over. This means that you have set the
path_checker
totur
, which works for all SCSI devices that support the Test Unit Ready command, which most do.
If the device needs a special command to switch paths, then configuring this device for multipath requires a hardware handler kernel module. The current available hardware handler is
emc
. If this is not sufficient for your device, you might not be able to configure the device for multipath.The following example shows a
device
entry in the multipath configuration file:# } # device { # vendor "COMPAQ " # product "MSA1000 " # path_grouping_policy multibus # path_checker tur # rr_weight priorities # } #}
Validate the
/etc/multipath.conf
file after modifying the multipath configuration file by running one of the following commands:To display any configuration errors, run:
# multipath -t > /dev/null
To display the new configuration with the changes added, run:
# multipath -t
Reload the
/etc/multipath.conf
file and reconfigure themultipathd
daemon for changes to take effect:# service multipathd reload
Additional resources
-
multipath.conf(5)
andmultipathd(8)
man pages
5.11. Setting multipath values for all devices
Using the overrides
section of the multipath.conf
configuration file, you can set a configuration value for all of your devices. This section supports all attributes that are supported by both the devices
and defaults
section of the multipath.conf
configuration file, which is all of the devices
section attributes except vendor
, product
, and revision
.
DM Multipath uses these attributes for all devices unless they are overwritten by the attributes specified in the multipaths
section of the multipath.conf
file for paths that contain the device. These attributes override the attributes set in the devices
and defaults
sections of the multipath.conf
file.
Procedure
Override device specific settings. For example, you might want all devices to set
no_path_retry
tofail
. Use the following command to turn off queueing, when all paths have failed. This overrides any device specific settings.overrides { no_path_retry fail }
Validate the
/etc/multipath.conf
file after modifying the multipath configuration file by running one of the following commands:To display any configuration errors, run:
# multipath -t > /dev/null
To display the new configuration with the changes added, run:
# multipath -t
Reload the
/etc/multipath.conf
file and reconfigure themultipathd
daemon for changes to take effect:# service multipathd reload
Additional resources
-
multipath.conf(5)
man page
Chapter 6. Preventing devices from multipathing
You can configure DM Multipath to ignore selected devices when it configures multipath devices. DM Multipath does not group these ignored devices into a multipath device.
6.1. Conditions when DM Multipath creates a multipath device for a path
DM Multipath has a set of default rules to determine whether to create a multipath device for a path or whether to ignore the path. You can configure the behavior.
If the find_multipaths
configuration parameter is set to off
, multipath always tries to create a multipath device for every path that is not explicitly disabled. If the find_multipaths
configuration parameter is set to on
, then multipath creates a device, only if one of following conditions is met:
- There are at least two paths with the same World-Wide Identification (WWID) that are not disabled.
-
You manually force the creation of the device by specifying a device with the
multipath
command. - A path has the same WWID as a multipath device that was previously created even if that multipath device does not currently exist. Whenever a multipath device is created, multipath remembers the WWID of the device so that it automatically creates the device again as soon as it sees a path with that WWID. This allows you to have multipath automatically choose the correct paths to make into multipath devices, without having to disable multipathing on other devices.
If you have previously created a multipath device without using the find_multipaths
parameter and then you later set the parameter to on
, you might need to remove the WWIDs of any device you do not want created as a multipath device from the /etc/multipath/wwids
file. The following example shows a sample /etc/multipath/wwids
file. The WWIDs are enclosed by slashes (/
):
# Multipath wwids, Version : 1.0 # NOTE: This file is automatically maintained by multipath and multipathd. # You should not need to edit this file in normal circumstances. # # Valid WWIDs: /3600d0230000000000e13955cc3757802/ /3600d0230000000000e13955cc3757801/ /3600d0230000000000e13955cc3757800/ /3600d02300069c9ce09d41c31f29d4c00/ /SWINSYS SF2372 0E13955CC3757802/ /3600d0230000000000e13955cc3757803/
In addition to on
and off
, you can also set find_multipaths
to the following values:
strict
-
Multipath never accepts paths that have not previously been multipathed and are therefore not in the
/etc/multipath/wwids
file. smart
-
Multipath always accepts non-disabled devices in
udev
as soon as they appear. Ifmultipathd
does not create the device within a timeout set with thefind_multipaths_timeout
parameter, it will release its claim on the device.
The built-in default value of find_multipaths
is off
. The default multipath.conf
file created by mpathconf
, however, will set the value of find_multipaths
to on
.
When the find_multipaths
parameter is set to on
, disable multipathing only on the devices with multiple paths that you do not want to be multipathed. Because of this, it will generally not be necessary to disable multipathing on devices.
If you add a previously created multipath device to blacklist
, removing the WWID of that device from the /etc/multipath/wwids
file by using the -w
option can help avoid issues with other programs. For example, to remove the device /dev/sdb
with WWID 3600d0230000000000e13954ed5f89300
from the /etc/multipath/wwids
file, you can use either of the following methods.
Removing a multipath device by using the device name.
# multipath -w /dev/sdb wwid '3600d0230000000000e13954ed5f89300' removed
Removing a multipath device by using the WWID of the device.
# multipath -w 3600d0230000000000e13954ed5f89300 wwid '3600d0230000000000e13954ed5f89300' removed
You can also use the -W
option to update the /etc/multipath/wwids
file. This would reset the /etc/multipath/wwids
file to only include the WWIDs of the current multipath devices. To reset the file, run the following:
# multipath -W
successfully reset wwids
Additional resources
-
multipath.conf(5)
man page
6.2. Criteria for disabling multipathing on certain devices
You can disable multipathing on devices by any of the following criteria:
- WWID
- device name
- device type
- property
- protocol
For every device, DM Multipath evaluates these criteria in the following order:
-
property
-
devnode
-
device
-
protocol
-
wwid
If a device turns out to be disabled by any of the mentioned criteria, DM Multipath excludes it from handling by multipathd
, and does not evaluate the later criteria. For each criteria, the exception list takes precedence over the list of disabled devices, if a device matches both.
By default, a variety of device types are disabled, even after you comment out the initial blacklist
section of the configuration file.
Additional resources
6.3. Disabling multipathing by WWID
You can disable multipathing on individual devices by their World-Wide Identification (WWID).
Procedure
Find WWID of a device:
# multipathd show paths raw format "%d %w" | grep sdb sdb 3600508b4001080520001e00011700000
Disable devices in the
/etc/multipath.conf
configuration file using thewwid
entry.The following example shows the lines in the DM Multipath configuration file that disable a device with a WWID of
3600508b4001080520001e00011700000
:blacklist { wwid 3600508b4001080520001e00011700000 }
Validate the
/etc/multipath.conf
file after modifying the multipath configuration file by running one of the following commands:To display any configuration errors, run:
# multipath -t > /dev/null
To display the new configuration with the changes added, run:
# multipath -t
Reload the
/etc/multipath.conf
file and reconfigure themultipathd
daemon for changes to take effect:# service multipathd reload
6.4. Disabling multipathing by device name
You can disable multipathing on device types by device name, so that DM Multipath will not group them into a multipath device.
Procedure
Display device information:
# udevadm info --query=all -n /dev/mapper/sd*
Disable devices in the
/etc/multipath.conf
configuration file using thedevnode
entry.The following example shows the lines in the DM Multipath configuration file that disable all SCSI devices, because it disables all
sd*
devices as well:blacklist { devnode "^sd[a-z]" }
You can use a
devnode
entry to disable individual devices rather than all devices of a specific type. However, this is not recommended because unless it is statically mapped byudev
rules, there is no guarantee that a specific device will have the same name on reboot. For example, a device name could change from/dev/sda
to/dev/sdb
on reboot.By default, DM Multipath disables all devices that are not SCSI, NVMe, or DASD, using the following
devnode
entry:blacklist { devnode "!^(sd[a-z]|dasd[a-z]|nvme[0-9])" }
The devices that this entry disables do not generally support DM Multipath.
Validate the
/etc/multipath.conf
file after modifying the multipath configuration file by running one of the following commands:To display any configuration errors, run:
# multipath -t > /dev/null
To display the new configuration with the changes added, run:
# multipath -t
Reload the
/etc/multipath.conf
file and reconfigure themultipathd
daemon for changes to take effect:# service multipathd reload
Additional resources
6.5. Disabling multipathing by device type
You can disable multipathing on devices by using the device section.
Procedure
Display device type:
# multipathd show paths raw format "%d %s" | grep sdb sdb HP,HSV210
Disable devices in the
/etc/multipath.conf
configuration file using thedevice
section.The following example disables multipathing on all IBM DS4200 and HP devices:
blacklist { device { vendor "IBM" product "3S42" #DS4200 Product 10 } device { vendor "HP" product ".*" } }
Validate the
/etc/multipath.conf
file after modifying the multipath configuration file by running one of the following commands:To display any configuration errors, run:
# multipath -t > /dev/null
To display the new configuration with the changes added, run:
# multipath -t
Reload the
/etc/multipath.conf
file and reconfigure themultipathd
daemon for changes to take effect:# service multipathd reload
6.6. Disabling multipathing by udev property
You can disable multipathing on devices by their udev
property parameter.
Procedure
Display the
udev
variables for a device:# udevadm info --query=all -n /dev/sdb
Disable devices in the
/etc/multipath.conf
configuration file using theproperty
parameter. This parameter is a regular expression string that matches against theudev
environment variable name for the devices.The following example disables multipathing on all devices with the
udev
propertyID_ATA
:blacklist { property "ID_ATA" }
Validate the
/etc/multipath.conf
file after modifying the multipath configuration file by running one of the following commands:To display any configuration errors, run:
# multipath -t > /dev/null
To display the new configuration with the changes added, run:
# multipath -t
Reload the
/etc/multipath.conf
file and reconfigure themultipathd
daemon for changes to take effect:# service multipathd reload
6.7. Disabling multipathing by device protocol
You can disable multipathing on devices by using device protocol.
Procedure
Optional: View the protocol that a path is using:
# multipathd show paths raw format "%d %P" | grep sdb sdb scsi:fcp
Disable devices in the
/etc/multipath.conf
configuration file using theprotocol
parameter.The protocol parameter takes a regular expression and blacklists all devices with matching protocol strings. For example, to disable multipathing on all nvme devices, use the following:
blacklist { protocol "nvme" }
DM Multipath recognizes the following protocol strings:
-
scsi:fcp
-
scsi:spi
-
scsi:ssa
-
scsi:sbp
-
scsi:srp
-
scsi:iscsi
-
scsi:sas
-
scsi:adt
-
scsi:ata
-
scsi:unspec
-
ccw
-
cciss
-
nvme:pcie
-
nvme:rdma
-
nvme:fc
-
nvme:tcp
-
nvme:loop
-
nvme:apple-nvme
-
nvme:unspec
-
undef
-
Validate the
/etc/multipath.conf
file after modifying the multipath configuration file by running one of the following commands:To display any configuration errors, run:
# multipath -t > /dev/null
To display the new configuration with the changes added, run:
# multipath -t
Reload the
/etc/multipath.conf
file and reconfigure themultipathd
daemon for changes to take effect:# service multipathd reload
6.8. Adding exceptions for devices with disabled multipathing
You can enable multipathing by adding exceptions on devices where multipathing is currently disabled.
Prerequisites
- Multipathing is disabled on certain devices.
Procedure
Enable multipathing on the devices using the
blacklist_exceptions
section of the/etc/multipath.conf
configuration file.When specifying devices in the
blacklist_exceptions
section of the configuration file, you must specify the exceptions using the same criteria as they were specified in theblacklist
section. For example, a WWID exception does not apply to devices disabled by adevnode
entry, even if the disabled device is associated with that WWID. Similarly,devnode
exceptions apply only todevnode
entries, anddevice
exceptions apply only to device entries.Example 6.1. An exception by WWID
If you have a large number of devices and want to multipath only one of them with the WWID of
3600d0230000000000e13955cc3757803
, instead of individually disabling each of the devices except the one you want, you could disable all of them, and then enable only the one you want by adding the following lines to the/etc/multipath.conf
file:blacklist { wwid ".*" } blacklist_exceptions { wwid "3600d0230000000000e13955cc3757803" }
Alternatively, you could use an exclamation mark (
!
) to invert theblacklist
entry, which disables all devices except the specified WWID:blacklist { wwid "!3600d0230000000000e13955cc3757803" }
Example 6.2. An exception by udev property
The
property
parameter works differently than the otherblacklist_exception
parameters. The value of theproperty
parameter must match the name of a variable in theudev
database. Otherwise, the device is disabled. Using this parameter, you can disable multipathing on certain SCSI devices, such as USB sticks and local hard drives.To enable multipathing only on SCSI devices that could reasonably be multipathed, set this parameter to
(SCSI_IDENT_|ID_WWN)
as in the following example:blacklist_exceptions { property "(SCSI_IDENT_|ID_WWN)" }
Validate the
/etc/multipath.conf
file after modifying the multipath configuration file by running one of the following commands:To display any configuration errors, run:
# multipath -t > /dev/null
To display the new configuration with the changes added, run:
# multipath -t
Reload the
/etc/multipath.conf
file and reconfigure themultipathd
daemon for changes to take effect:# service multipathd reload
Chapter 7. Managing multipathed volumes
The following are a few commands provided by DM Multipath, which you can use to manage multipath volumes:
-
multipath
-
dmsetup
-
multipathd
7.1. Resizing an online multipath device
If you need to resize an online multipath device, use the following procedure.
Procedure
- Resize your physical device.
Execute the following command to find the paths to the logical unit number (LUN):
#
multipath -l
Resize your paths. For SCSI devices, writing a 1 to the
rescan
file for the device causes the SCSI driver to rescan, as in the following command:#
echo 1 > /sys/block/path_device/device/rescan
Ensure that you run this command for each of the path devices. For example, if your path devices are
sda
,sdb
,sde
, andsdf
, you would run the following commands:#
echo 1 > /sys/block/sda/device/rescan
#echo 1 > /sys/block/sdb/device/rescan
#echo 1 > /sys/block/sde/device/rescan
#echo 1 > /sys/block/sdf/device/rescan
Resize your multipath device:
#
multipathd resize map multipath_device
Resize the file system (assuming no LVM or DOS partitions are used):
#
resize2fs /dev/mapper/mpatha
7.2. Moving a root file system from a single path device to a multipath device
If you have installed your system on a single-path device and later add another path to the root file system, you will need to move your root file system to a multipathed device. See the following procedure for moving from a single-path to a multipathed device.
Prerequisites
-
You have installed the
device-mapper-multipath
package.
Procedure
Create the
/etc/multipath.conf
configuration file, load the multipath module, and enable themultipathd
systemd
service:# dnf install device-mapper-multipath
Execute the following command to create the
/etc/multipath.conf
configuration file, load the multipath module, and setchkconfig
for themultipathd
toon
:# mpathconf --enable
-
If the
find_multipaths
configuration parameter is not set toyes
, edit theblacklist
andblacklist_exceptions
sections of the/etc/multipath.conf
file, as described in Preventing devices from multipathing. In order for multipath to build a multipath device on top of the root device as soon as it is discovered, enter the following command. This command also ensures that
find_multipaths
allows the device, even if it only has one path.# multipath -a root_devname
For example, if the root device is
/dev/sdb
, enter the following command.#
multipath -a /dev/sdb
wwid '3600d02300069c9ce09d41c4ac9c53200' added
Confirm that your configuration file is set up correctly by executing the
multipath
command and search the output for a line of the following format. This indicates that the command failed to create the multipath device.date wwid: ignoring map
For example, if the WWID of the device is 3600d02300069c9ce09d41c4ac9c53200, you would see a line in the output such as the following:
# multipath Oct 21 09:37:19 | 3600d02300069c9ce09d41c4ac9c53200: ignoring map
Rebuild the
initramfs
file system withmultipath
:# dracut --force -H --add multipath
- Shut the machine down.
- Boot the machine.
- Make the other paths visible to the machine.
Verification
Check whether the multipath device is created by running the following command:
# multipath -l | grep 3600d02300069c9ce09d41c4ac9c53200 mpatha (3600d02300069c9ce09d41c4ac9c53200) dm-0 3PARdata,VV
7.3. Moving a swap file system from a single path device to a multipath device
By default, swap devices are set up as logical volumes. This does not require any special procedure for configuring them as multipath devices as long as you set up multipathing on the physical volumes that constitute the logical volume group. If your swap device is not an LVM volume, however, and it is mounted by device name, you might need to edit the /etc/fstab
file to switch to the appropriate multipath device name.
Procedure
Add the WWID of the device to the
/etc/multipath/wwids
file:# multipath -a swap_devname
For example, if the root device is
/dev/sdb
, enter the following command.# multipath -a /dev/sdb wwid '3600d02300069c9ce09d41c4ac9c53200' added
Confirm that your configuration file is set up correctly by executing the
multipath
command and search the output for a line of the following format:date wwid: ignoring map
This indicates that the command failed to create the multipath device.
For example, if the WWID of the device is 3600d02300069c9ce09d41c4ac9c53200, you would see a line in the output such as the following:
#
multipath
Oct 21 09:37:19 | 3600d02300069c9ce09d41c4ac9c53200: ignoring mapSet up an alias for the swap device in the
/etc/multipath.conf
file:multipaths { multipath { wwid WWID_of_swap_device alias swapdev } }
Edit the
/etc/fstab
file and replace the old device path to the root device with the multipath device.For example, if you had the following entry in the
/etc/fstab
file:/dev/sdb2 swap swap defaults 0 0
Change the entry to the following:
/dev/mapper/swapdev swap swap defaults 0 0
Rebuild the initramfs file system with multipath:
# dracut --force -H --add multipath
- Shut the machine down.
- Boot the machine.
- Make the other paths visible to the machine.
Verification
Verify if the swap device is on the multipath device:
# swapon -s
For example:
# swapon -s Filename Type Size Used Priority /dev/dm-3 partition 4169724 0 -2
The file name should match the multipath swap device.
# readlink -f /dev/mapper/swapdev /dev/dm-3
7.4. Determining device mapper entries with the dmsetup command
You can use the dmsetup
command to find out which device mapper entries match the multipathed devices.
Procedure
Display all the device mapper devices and their major and minor numbers. The minor numbers determine the name of the dm device. For example, a minor number of 3 corresponds to the multipathed device
/dev/dm-3
.#
dmsetup ls
mpathd (253:4) mpathep1 (253:12) mpathfp1 (253:11) mpathb (253:3) mpathgp1 (253:14) mpathhp1 (253:13) mpatha (253:2) mpathh (253:9) mpathg (253:8) VolGroup00-LogVol01 (253:1) mpathf (253:7) VolGroup00-LogVol00 (253:0) mpathe (253:6) mpathbp1 (253:10) mpathd (253:5)
7.5. Administering the multipathd daemon
The multipathd
commands can be used to administer the multipathd
daemon.
Procedure
View the default format for the output of the
multipathd show maps
command:# multipathd show maps name sysfs uuid mpathc dm-0 360a98000324669436c2b45666c567942
Some
multipathd
commands include aformat
option followed by a wildcard. Display a list of available wildcards with the following command:# multipathd show wildcards multipath format wildcards: %n name %w uuid %d sysfs ...
Display the multipath devices that
multipathd
is monitoring. Use wildcards to specify the shown fields:# multipathd show maps format "%n %w %d %s" name uuid sysfs vend/prod/rev mpathc 360a98000324669436c2b45666c567942 dm-0 NETAPP,LUN
Display the paths that
multipathd
is monitoring. Use wildcards to specify the shown fields:# multipathd show paths format "%n %w %d %s" target WWNN uuid dev vend/prod/rev 0x50001fe1500d2250 3600508b4001080520001e00011700000 sdb HP,HSV210
Display data in a raw format:
# multipathd show maps raw format "%n %w %d %s" mpathc 360a98000324669436c2b45666c567942 dm-0 NETAPP,LUN
In raw format, no headers are printed and the fields are not padded to align the columns with the headers. This output can be more easily used for scripting.
Additional resources
-
multipathd
(8) man page
Chapter 8. Removing storage devices
You can safely remove a storage device from a running system, which helps prevent system memory overload and data loss.
Prerequisites
Before you remove a storage device, you must ensure that you have enough free system memory due to the increased system memory load during an I/O flush. Use the following commands to view the current memory load and free memory of the system:
# vmstat 1 100 # free
Red Hat does not recommend removing a storage device on a system where:
- Free memory is less than 5% of the total memory in more than 10 samples per 100.
-
Swapping is active (non-zero
si
andso
columns in thevmstat
command output).
8.1. Safe removal of storage devices
Safely removing a storage device from a running system requires a top-to-bottom approach. Start from the top layer, which typically is an application or a file system, and work towards the bottom layer, which is the physical device.
You can use storage devices in multiple ways, and they can have different virtual configurations on top of physical devices. For example, you can group multiple instances of a device into a multipath device, make it part of a RAID, or you can make it part of an LVM group. Additionally, devices can be accessed via a file system, or they can be accessed directly such as a “raw” device.
While using the top-to-bottom approach, you must ensure that:
- the device that you want to remove is not in use
- all pending I/O to the device is flushed
- the operating system is not referencing the storage device
8.2. Removing block devices and associated metadata
To safely remove a block device from a running system, to help prevent system memory overload and data loss you need to first remove metadata from them. Address each layer in the stack, starting with the file system, and proceed to the disk. These actions prevent putting your system into an inconsistent state.
Use specific commands that may vary depending on what type of devices you are removing:
-
lvremove
,vgremove
andpvremove
are specific to LVM. -
For software RAID, run
mdadm
to remove the array. For more information, see Managing RAID. - For block devices encrypted using LUKS, there are specific additional steps. The following procedure will not work for the block devices encrypted using LUKS. For more information, see Encrypting block devices using LUKS.
Rescanning the SCSI bus or performing any other action that changes the state of the operating system, without following the procedure documented here can cause delays due to I/O timeouts, devices to be removed unexpectedly, or data loss.
Prerequisites
- You have an existing block device stack containing the file system, the logical volume, and the volume group.
- You ensured that no other applications or services are using the device that you want to remove.
- You backed up the data from the device that you want to remove.
Optional: If you want to remove a multipath device, and you are unable to access its path devices, disable queueing of the multipath device by running the following command:
# multipathd disablequeueing map multipath-device
This enables the I/O of the device to fail, allowing the applications that are using the device to shut down.
Removing devices with their metadata one layer at a time ensures no stale signatures remain on the disk.
Procedure
Unmount the file system:
# umount /mnt/mount-point
Remove the file system:
# wipefs -a /dev/vg0/myvol
NoteIf you have added an entry into
/etc/fstab
file to make a persistent association between the file system and a mount point you should also edit/etc/fstab
at this point to remove that entry.Continue with the following steps, depending on the type of the device you want to remove:
Remove the logical volume (LV) that contained the file system:
# lvremove vg0/myvol
If there are no other logical volumes remaining in the volume group (VG), you can safely remove the VG that contained the device:
# vgremove vg0
Remove the physical volume (PV) metadata from the PV device(s):
# pvremove /dev/sdc1
# wipefs -a /dev/sdc1
Remove the partitions that contained the PVs:
# parted /dev/sdc rm 1
Follow the next steps only if you want to fully wipe the device.
Remove the partition table:
# wipefs -a /dev/sdc
Follow the next steps only if you want to physically remove the device.
If you are removing a multipath device, execute the following commands:
View all the paths to the device:
# multipath -l
The output of this command is required in a later step.
Flush the I/O and remove the multipath device:
# multipath -f multipath-device
If the device is not configured as a multipath device, or if the device is configured as a multipath device and you have previously passed I/O to the individual paths, flush any outstanding I/O to all device paths that are used:
# blockdev --flushbufs device
This is important for devices accessed directly where the
umount
orvgreduce
commands do not flush the I/O.If you are removing a SCSI device, execute the following commands:
-
Remove any reference to the path-based name of the device, such as
/dev/sd
,/dev/disk/by-path
, or themajor:minor
number, in applications, scripts, or utilities on the system. This ensures that different devices added in the future are not mistaken for the current device. Remove each path to the device from the SCSI subsystem:
# echo 1 > /sys/block/device-name/device/delete
Here the
device-name
is retrieved from the output of themultipath -l
command, if the device was previously used as a multipath device.
-
Remove any reference to the path-based name of the device, such as
- Remove the physical device from a running system. Note that the I/O to other devices does not stop when you remove this device.
Verification
Verify that the devices you intended to remove are not displaying on the output of
lsblk
command. The following is an example output:# lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 5G 0 disk sr0 11:0 1 1024M 0 rom vda 252:0 0 10G 0 disk |-vda1 252:1 0 1M 0 part |-vda2 252:2 0 100M 0 part /boot/efi `-vda3 252:3 0 9.9G 0 part /
Additional resources
-
The
multipath(8)
,pvremove(8)
,vgremove(8)
,lvremove(8)
,wipefs(8)
,parted(8)
,blockdev(8)
andumount(8)
man pages.
Chapter 9. Troubleshooting DM Multipath
If you have trouble implementing a multipath configuration, there are a variety of issues you can check for. The following issues may result in a slow or non-functioning multipath configuration:
- The multipath daemon is not running
-
If you find you have trouble implementing a multipath configuration, ensure that the
multipathd
daemon is running, as described in Configuring DM Multipath. Themultipathd
daemon must be running to use multipathed devices. - Issues with
queue_if_no_path
feature -
If a multipath device is configured with the
features "1 queue_if_no_path"
option, then any process that issues I/O hangs until one or more paths are restored.
9.1. Troubleshooting issues with queue_if_no_path feature
If a multipath device is configured with the features "1 queue_if_no_path"
option, then any process that issues I/O hangs until one or more paths are restored. To avoid this, set the no_path_retry N
parameter in the /etc/multipath.conf
file, where N is the number of times the system should retry a path.
To use the features "1 queue_if_no_path"
option without the described problem, you can disable the queueing policy at runtime for a particular LUN, for which all paths are unavailable.
Procedure
Disable queueing:
For a specific device:
# multipathd disablequeueing map device
For all devices:
# multipathd disablequeueing maps
After you disable queueing, it will remain disabled until you restart or reload
multipathd
.
Reset queueing to a previous value:
For a specific device:
# multipathd restorequeueing map device
For all devices:
# multipathd restorequeueing maps
9.2. Troubleshooting with the multipathd interactive console
The multipathd -k
command is an interactive interface to the multipathd
daemon. Entering this command brings up an interactive multipath console. After executing this command, you can enter help
to get a list of available commands and Ctrl+D to quit.
Use the multipathd
interactive console to troubleshoot problems you might have with your system.
Procedure
Display the multipath configuration, including the default values, before exiting the console:
# multipathd -k multipathd> show config multipathd> Ctrl+D
Ensure that multipath picked up all changes to the
multipath.conf
file:# multipathd -k multipathd> reconfigure multipathd> Ctrl+D
Ensure that the path checker is working properly:
# multipathd -k multipathd> show paths multipathd> Ctrl+D
You can also run a single
multipathd
interactive command directly from the command line, without starting the interactive console. For example, to check that multipath picks up all changes to themultipath.conf
file, run the following command:# multipathd reconfigure
Chapter 10. Configuring maximum time for storage error recovery with eh_deadline
You can configure the maximum allowed time to recover failed SCSI devices. This configuration guarantees an I/O response time even when storage hardware becomes unresponsive due to a failure.
10.1. The eh_deadline parameter
The SCSI error handling (EH) mechanism attempts to perform error recovery on failed SCSI devices. The SCSI host object eh_deadline
parameter enables you to configure the maximum amount of time for the recovery. After the configured time expires, SCSI EH stops and resets the entire host bus adapter (HBA).
Using eh_deadline
can reduce the time:
- to shut off a failed path,
- to switch a path, or
- to disable a RAID slice.
When eh_deadline
expires, SCSI EH resets the HBA, which affects all target paths on that HBA, not only the failing one. If some of the redundant paths are not available for other reasons, I/O errors might occur. Enable eh_deadline
only if you have multipath configured on all targets. Also, if your multipath devices are not fully redundant, you should verify that no_path_retry
is set large enough to allow paths to recover.
The value of the eh_deadline
parameter is specified in seconds. The default setting is off
, which disables the time limit and allows all of the error recovery to take place.
Scenarios when eh_deadline is useful
In most scenarios, you do not need to enable eh_deadline
. Using eh_deadline
can be useful in certain specific scenarios. For example if a link loss occurs between a Fibre Channel (FC) switch and a target port, and the HBA does not receive Registered State Change Notifications (RSCNs). In such a case, I/O requests and error recovery commands all time out rather than encounter an error. Setting eh_deadline
in this environment puts an upper limit on the recovery time. That enables the failed I/O to be retried on another available path by DM Multipath.
Under the following conditions, the eh_deadline
parameter provides no additional benefit, because the I/O and error recovery commands fail immediately, which enables DM Multipath to retry:
- If RSCNs are enabled
- If the HBA does not register the link becoming unavailable
10.2. Setting the eh_deadline parameter
This procedure configures the value of the eh_deadline
parameter to limit the maximum SCSI recovery time.
Procedure
You can configure
eh_deadline
using either of the following methods:defaults
section of themultpath.conf
fileFrom the defaults section of the
multpath.conf
file, set theeh_deadline
parameter to the required number of seconds:# eh_deadline 300
NoteFrom RHEL 8.4, setting the
eh_deadline
parameter using the defaults section of themultpath.conf
file is the preferred method.To turn off the
eh_deadline
parameter with this method, seteh_deadline
tooff
.sysfs
Write the number of seconds into the
/sys/class/scsi_host/host<host-number>/eh_deadline
files. For example, to set theeh_deadline
parameter throughsysfs
on SCSI host 6:# echo 300 > /sys/class/scsi_host/host6/eh_deadline
To turn off the
eh_deadline
parameter with this method, use echooff
.Kernel parameter
Set a default value for all SCSI HBAs using the
scsi_mod.eh_deadline
kernel parameter.# echo 300 > /sys/module/scsi_mod/parameters/eh_deadline
To turn off the
eh_deadline
parameter with this method, use echo-1
.
Additional resources