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Chapter 39. Modifying Link Loss Behavior
This section describes how to modify the link loss behavior of devices that use either fibre channel or iSCSI protocols.
39.1. 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. To verify if a device is blocked, run the following command:
$ cat /sys/block/device/device/state
This command will return
blocked if the device is blocked. If the device is operating normally, this command will return running.
Procedure 39.1. Determining The State of a Remote Port
- To determine the state of a remote port, run the following command:
$ cat /sys/class/fc_remote_port/rport-H:B:R/port_state
- This command will return
Blockedwhen the remote port (along with devices accessed through it) are blocked. If the remote port is operating normally, the command will returnOnline. - If the problem is not resolved within
dev_loss_tmoseconds, the rport and devices will be unblocked and all I/O running on that device (along with any new I/O sent to that device) will be failed.
Procedure 39.2. Changing dev_loss_tmo
- To change the
dev_loss_tmovalue,echoin the desired value to the file. For example, to setdev_loss_tmoto 30 seconds, run:$ echo 30 > /sys/class/fc_remote_port/rport-H:B:R/dev_loss_tmo
For more information about
dev_loss_tmo, refer to Section 26.1, “Fibre Channel API”.
When a link or target port loss exceeds
dev_loss_tmo, the scsi_device and sdN devices are removed. The target port SCSI ID binding is saved. When the target returns, the SCSI address and sdNassignments may be changed. The SCSI address will change if there has been any LUN configuration changes behind the target port. The sdN names may change depending on timing variations during the LUN discovery process or due to LUN configuration change within storage. These assignments are not persistent as described in Chapter 28, Persistent Naming. Refer to section Chapter 28, Persistent Naming for alternative device naming methods that are persistent.
