Chapter 10. Using Fibre Channel devices Red Hat Enterprise Linux 8 provides the following native Fibre Channel drivers: lpfc qla2xxx zfcp 10.1. Resizing Fibre Channel logical units As a system administrator, you can resize Fibre Channel logical units. Procedure Determine which devices are paths for a multipath logical unit: Re-scan Fibre Channel logical units on a system that uses multipathing: Additional resources multipath(8) man page on your system 10.2. 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: This command returns one of the following output: Blocked when the remote port along with devices accessed through it are blocked. Online if the remote port is operating normally If the problem is not resolved within dev_loss_tmo seconds, the rport and devices will be unblocked. All I/O running on that device along with any new I/O sent to that device will fail. 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 on your system Recommended tuning at scsi,multipath and at application layer while configuring Oracle RAC cluster (Red Hat Knowledgebase) 10.3. 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 Important 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/target H : 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/host H / port_id node_name port_name issue_lip Instructs the driver to rediscover remote ports. 10.4. 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_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.

Commands:
multipath -ll
echo 1 > /sys/block/ sdX /device/rescan
cat /sys/class/fc_remote_ports/rport- host : bus : remote-port /port_state