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Chapter 11. Using Fibre Channel devices
Red Hat Enterprise Linux 8 provides the following native Fibre Channel drivers:
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lpfc -
qla2xxx -
zfcp
11.1. Resizing Fibre Channel Logical Units
As a system administrator, you can resize Fibre Channel logical units.
Procedure
Determine which devices are paths for a
multipathlogical unit:multipath -ll
Re-scan Fibre Channel logical units on a system that uses multipathing:
$ echo 1 > /sys/block/sdX/device/rescan
Additional resources
-
multipath(8)man page
11.2. Determining the link loss behavior of device using Fibre Channel
If a driver implements the Transport dev_loss_tmo callback, access attempts to a device through a link will be blocked when a transport problem is detected.
Procedure
Determine the state of a remote port:
$ cat /sys/class/fc_remote_port/rport-host:bus:remote-port/port_state
This command returns any one of the following output:
-
Blockedwhen the remote port along with devices accessed through it are blocked. Onlineif the remote port is operating normallyIf the problem is not resolved within
dev_loss_tmoseconds, therportand devices will be unblocked. All I/O running on that device along with any new I/O sent to that device will fail.
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When a link loss exceeds dev_loss_tmo, the scsi_device and sd_N_ devices are removed. Typically, the Fibre Channel class will leave the device as is, that is /dev/sdx will remain /dev/sdx. This is because the target binding is saved by the Fibre Channel driver and when the target port returns, the SCSI addresses are recreated faithfully. However, this cannot be guaranteed, the sdx device will be restored only if no additional change on in-storage box configuration of LUNs is made.
Additional resources
-
multipath.conf(5)man page - Recommended tuning at scsi,multipath and at application layer while configuring Oracle RAC cluster Knowledgebase article
11.3. Fibre Channel configuration files
The following is the list of configuration files in the /sys/class/ directory that provide the user-space API to Fibre Channel.
The items use the following variables:
H- Host number
B- Bus number
T- Target
L- Logical unit (LUNs)
R- Remote port number
Consult your hardware vendor before changing any of the values described in this section, if your system is using multipath software.
Transport configuration in /sys/class/fc_transport/targetH:B:T/
port_id- 24-bit port ID/address
node_name- 64-bit node name
port_name- 64-bit port name
Remote port configuration in /sys/class/fc_remote_ports/rport-H:B-R/
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port_id -
node_name -
port_name dev_loss_tmoControls when the scsi device gets removed from the system. After
dev_loss_tmotriggers, the scsi device is removed. In themultipath.conffile , you can setdev_loss_tmotoinfinity.In Red Hat Enterprise Linux 8, if you do not set the
fast_io_fail_tmooption,dev_loss_tmois capped to600seconds. By default,fast_io_fail_tmois set to5seconds in Red Hat Enterprise Linux 8 if themultipathdservice is running; otherwise, it is set tooff.fast_io_fail_tmoSpecifies the number of seconds to wait before it marks a link as "bad". Once a link is marked bad, existing running I/O or any new I/O on its corresponding path fails.
If I/O is in a blocked queue, it will not be failed until
dev_loss_tmoexpires and the queue is unblocked.If
fast_io_fail_tmois set to any value except off,dev_loss_tmois uncapped. Iffast_io_fail_tmois set to off, no I/O fails until the device is removed from the system. Iffast_io_fail_tmois set to a number, I/O fails immediately when thefast_io_fail_tmotimeout triggers.
Host configuration in /sys/class/fc_host/hostH/
-
port_id -
node_name -
port_name issue_lipInstructs the driver to rediscover remote ports.
11.4. 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_timeoutconfiguration option globally overrides therecovery_tmovalue for all iSCSI devices. For all iSCSI devices that are managed by DM Multipath, the
fast_io_fail_tmooption in DM Multipath globally overrides therecovery_tmovalue.The
fast_io_fail_tmooption in DM Multipath also overrides thefast_io_fail_tmooption 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.
