Configuring device mapper multipath

Procedure

1. 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 status

       For more information about the dm, path and online status, see Path status.

Procedure

1. 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

2. If your system does not include the package, install it by running the following command:

   # yum install device-mapper-multipath

Procedure

1. Enable and initialize the multipath configuration file:

   # mpathconf --enable

2. Optional: Edit the /etc/multipath.conf file.

   Most default settings are already configured, including path_grouping_policy which is set to failover.

3. Optional: The default naming format of multipath devices is set to /dev/mapper/mpathn format. If you prefer a different naming format:

   1. 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

   2. Reload the configuration of the DM Multipath daemon:

      # systemctl reload multipathd.service

4. Start the DM Multipath daemon:

   # systemctl start multipathd.service

Procedure

1. 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 is WDC_WD800JD-75MSA3_WD-WMAM9FU71040.

2. 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
   }

   Warning

   Although you could identify the device using its devnode parameter, such as sda, it would not be a safe procedure, because /dev/sda is not guaranteed to refer to the same device on reboot.

3. 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

4. If the disk is included in initramfs remake the initramfs. For more information see Configuring multipathing in initramfs.

5. Reload the /etc/multipath.conf file by reconfiguring the multipathd daemon:

   # systemctl reload multipathd

Verification

1. 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

Procedure

1. View the default configuration value and supported devices:

   # multipathd show config

2. 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
       }
   }

3. Save your changes and close the editor.

4. Update the multipath device list by scanning for new devices:

   # multipath -r

Procedure

1. 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 the initramfs for the changes to tale effect. If your root device employs multipath, the dracut command will automatically include the multipath module in the initramfs.

2. Optional: If multipath in the initramfs is no longer necessary:

   1. Remove the multipath configuration file:

      # rm /etc/dracut.conf.d/multipath.conf

   2. Rebuild the initramfs with the added multipath configuration:

      # dracut --force --omit multipath

Procedure

1. 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.

2. If native NVMe multipathing is disabled, enable it by using one of the following methods:

   • Using a kernel option:

     1. Add the nvme_core.multipath=Y option to the command line:

        # grubby --update-kernel=ALL --args="nvme_core.multipath=Y"

     2. On the 64-bit IBM Z architecture, update the boot menu:

        # zipl

     3. Reboot the system.

   • Using a kernel module configuration file:

     1. Create the /etc/modprobe.d/nvme_core.conf configuration file with the following content:

        options nvme_core multipath=Y

     2. Back up the initramfs file:

        # cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).bak.$(date +%m-%d-%H%M%S).img

     3. Rebuild the initramfs:

        # dracut --force --verbose

     4. Reboot the system.

3. 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

4. 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

1. 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

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, and nvme tcp indicates that the device is connected over TCP.

3. 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

4. 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

Procedure

1. Check if the native NVMe multipathing is disabled:

   # 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.

2. If the native NVMe multipathing is enabled, disable it by using one of the following methods:

   • Using a kernel option:

     1. Remove the nvme_core.multipath=Y option from the kernel command line:

        # grubby --update-kernel=ALL --remove-args="nvme_core.multipath=Y"

     2. On the 64-bit IBM Z architecture, update the boot menu:

        # zipl

     3. Reboot the system.

   • Using a kernel module configuration file:

     1. Remove the nvme_core multipath=Y option line from the /etc/modprobe.d/nvme_core.conf file, if it is present.

     2. Back up the initramfs file:

        # cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).bak.$(date +%m%d-%H%M%S).img

     3. Rebuild the initramfs:

        # cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).bak.$(date +%m-%d-%H%M%S).img
        # dracut --force --verbose

     4. Reboot the system.

3. Enable DM Multipath:

   # systemctl enable --now multipathd.service

4. 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
           }
   }

   Note

   The /sys/class/nvme-subsystem/nvme-subsys0/iopolicy configuration file has no effect on the I/O distribution when DM Multipath manages the NVMe devices.

5. Reload the multipathd service to apply the configuration changes:

   # multipath -r

1. multipaths section
2. overrides section
3. devices section
4. defaults section

Procedure

1. 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
   #}

2. 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 to multibus instead of the default value of failover, 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
   }

3. 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

4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload

Procedure

1. 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 of yellow.
   • The second multipath device in the example has a WWID of 1DEC_321816758474 and a symbolic name of red.

   In this example, the rr_weight attribute is set to priorities.

   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
           }
   }

2. 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

3. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload

Procedure

1. 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

2. Edit the overrides section of the /etc/multipath.conf file, by adding protocol 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
             }
     }

Procedure

1. 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.

2. 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.

3. Add a device that is not configured automatically by default to the devices section of the configuration file by setting the vendor and product 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

4. 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 to multibus. Other parameters you may need to set are no_path_retry and rr_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 to tur, 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
   #	}
   #}

5. 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

6. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload

Procedure

1. Override device specific settings. For example, you might want all devices to set no_path_retry to fail. Use the following command to turn off queueing, when all paths have failed. This overrides any device specific settings.

   overrides {
           no_path_retry fail
   }

2. 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

3. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload

1. property
2. devnode
3. device
4. protocol
5. wwid

Procedure

1. Find WWID of a device:

   # multipathd show paths raw format "%d %w" | grep sdb
   sdb 3600508b4001080520001e00011700000

2. Disable devices in the /etc/multipath.conf configuration file using the wwid 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
   }

3. 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

4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload

Procedure

1. Display device information:

   # udevadm info --query=all -n /dev/mapper/sd* 

2. Disable devices in the /etc/multipath.conf configuration file using the devnode 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 by udev 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.

3. 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

4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload

Procedure

1. Display device type:

   # multipathd show paths raw format "%d %s" | grep sdb
   sdb HP,HSV210

2. Disable devices in the /etc/multipath.conf configuration file using the device 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 ".*"
          }
   }

3. 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

4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload

Procedure

1. Display the udev variables for a device:

   # udevadm info --query=all -n /dev/sdb

2. Disable devices in the /etc/multipath.conf configuration file using the property parameter. This parameter is a regular expression string that matches against the udev environment variable name for the devices.

   The following example disables multipathing on all devices with the udev property ID_ATA:

   blacklist {
           property "ID_ATA"
   }

3. 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

4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload

Procedure

1. Optional: View the protocol that a path is using:

   # multipathd show paths raw format "%d %P" | grep sdb
   sdb scsi:fcp

2. Disable devices in the /etc/multipath.conf configuration file using the protocol 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

3. 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

4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload

Procedure

1. 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 the blacklist section. For example, a WWID exception does not apply to devices disabled by a devnode entry, even if the disabled device is associated with that WWID. Similarly, devnode exceptions apply only to devnode entries, and device 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 the blacklist 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 other blacklist_exception parameters. The value of the property parameter must match the name of a variable in the udev 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)"
   }

2. 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

3. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect:

   # service multipathd reload

Procedure

1. Resize your physical device.

2. Execute the following command to find the paths to the logical unit number (LUN):

   # multipath -l

3. 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, and sdf, 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

4. Resize your multipath device:

   # multipathd resize map multipath_device

5. Resize the file system (assuming no LVM or DOS partitions are used):

   # resize2fs /dev/mapper/mpatha

Procedure

1. Create the /etc/multipath.conf configuration file, load the multipath module, and enable the multipathd systemd service:

   # yum install device-mapper-multipath

2. Execute the following command to create the /etc/multipath.conf configuration file, load the multipath module, and set chkconfig for the multipathd to on:

   # mpathconf --enable

3. If the find_multipaths configuration parameter is not set to yes, edit the blacklist and blacklist_exceptions sections of the /etc/multipath.conf file, as described in Preventing devices from multipathing.

4. 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

5. 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

6. Rebuild the initramfs file system with multipath:

   # dracut --force -H --add multipath

7. Shut the machine down.
8. Boot the machine.
9. Make the other paths visible to the machine.

Procedure

1. 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

2. 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 map

3. Set up an alias for the swap device in the /etc/multipath.conf file:

   multipaths {
       multipath {
           wwid WWID_of_swap_device
           alias swapdev
       }
   }

4. 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

5. Rebuild the initramfs file system with multipath:

   # dracut --force -H --add multipath

6. Shut the machine down.
7. Boot the machine.
8. Make the other paths visible to the machine.

Procedure

1. Unmount the file system:

   # umount /mnt/mount-point

2. Remove the file system:

   # wipefs -a /dev/vg0/myvol

   Note

   If 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:

3. Remove the logical volume (LV) that contained the file system:

   # lvremove vg0/myvol

4. 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

5. Remove the physical volume (PV) metadata from the PV device(s):

   # pvremove /dev/sdc1

   # wipefs -a /dev/sdc1

6. Remove the partitions that contained the PVs:

   # parted /dev/sdc rm 1

7. Remove the partition table:

   # wipefs -a /dev/sdc

8. Remove the physical device from a running system. Note that the I/O to other devices does not stop when you remove this device.

Procedure

1. 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.

2. Reset queueing to a previous value:

   • For a specific device:

     # multipathd restorequeueing map device

   • For all devices:

     # multipathd restorequeueing maps

Procedure

1. Display the multipath configuration, including the default values, before exiting the console:

   # multipathd -k
   multipathd> show config
   multipathd> Ctrl+D

2. Ensure that multipath picked up all changes to the multipath.conf file:

   # multipathd -k
   multipathd> reconfigure
   multipathd> Ctrl+D

3. Ensure that the path checker is working properly:

   # multipathd -k
   multipathd> show paths
   multipathd> Ctrl+D

4. 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 the multipath.conf file, run the following command:

   # multipathd reconfigure