Chapter 8. Using Fibre Channel devices

RHEL 8 provides the following native Fibre Channel drivers:

  • lpfc
  • qla2xxx
  • zfcp

8.1. Resizing Fibre Channel Logical Units

As a system administrator, you can resize Fibre Channel logical units.

Procedure

  1. To determine which devices are paths for a multipath logical unit:

    multipath -ll
  2. To re-scan Fibre Channel logical units on a system that uses multipathing:

    $ echo 1 > /sys/block/sdX/device/rescan

Additional resources

  • The multipath man page.

8.3. Fibre Channel configuration files

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
Important

If your system is using multipath software, Red Hat recommends that you consult your hardware vendor before changing any of the values described in this section.

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/

  • port_id
  • node_name
  • port_name
  • dev_loss_tmo

    Controls when the scsi device gets removed from the system. After dev_loss_tmo triggers, the scsi device is removed. In the multipath.conf file , you can set dev_loss_tmo to infinity.

    In Red Hat Enterprise Linux 8, if you do not set the fast_io_fail_tmo option, dev_loss_tmo is capped to 600 seconds. By default, fast_io_fail_tmo is set to 5 seconds in Red Hat Enterprise Linux 8 if the multipathd service is running; otherwise, it is set to off.

  • fast_io_fail_tmo

    Specifies 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_tmo expires and the queue is unblocked.

    If fast_io_fail_tmo is set to any value except off, dev_loss_tmo is uncapped. If fast_io_fail_tmo is set to off, no I/O fails until the device is removed from the system. If fast_io_fail_tmo is set to a number, I/O fails immediately when the fast_io_fail_tmo timeout triggers.

Host configuration in /sys/class/fc_host/hostH/

  • port_id
  • node_name
  • port_name
  • issue_lip

    Instructs the driver to rediscover remote ports.

8.4. 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 recovery_tmo values:

  • The replacement_timeout configuration option globally overrides the recovery_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 the recovery_tmo value.

    The fast_io_fail_tmo option in DM Multipath also overrides the fast_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.