Fibre Channel - Red Hat ENTERPRISE LINUX 5.5 - ONLINE STORAGE GUIDE Manual

Online Storage Guide

16.1. 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 5. Determining The State of a Remote Port
1. To determine the state of a remote port, run the following command:
cat /sys/class/fc_remote_port/rport-H:B:R/port_state
2. This command will return Blocked when the remote port (along with devices accessed through
it) are blocked. If the remote port is operating normally, the command will return Online.
3. If the problem is not resolved within dev_loss_tmo seconds, the rport and devices will be
unblocked and all IO running on that device (along with any new IO sent to that device) will be
failed.
Procedure 6. Changing dev_loss_tmo
• To change the dev_loss_tmo value, echo in the desired value to the file. For example, to set
dev_loss_tmo to 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
When a device is blocked, the fibre channel class will leave the device as is; i.e. /dev/sdx will remain
/dev/sdx. This is because the dev_loss_tmo expired. If the link problem is fixed at a later time,
operations will continue using the same SCSI device and device node name.
Fibre Channel: remove_on_dev_loss
If you prefer that devices are removed at the SCSI layer when links are marked bad (i.e. expired
after dev_loss_tmo seconds), you can use the scsi_transport_fc module parameter
remove_on_dev_loss. When a device is removed at the SCSI layer while remove_on_dev_loss
is in effect, the device will be added back once all transport problems are corrected.
Warning
The use of remove_on_dev_loss is not recommended, as removing a device at the
SCSI layer does not automatically unmount any file systems from that device. When
file systems from a removed device are left mounted, the device may not be properly
removed from multipath or RAID devices.
Further problems may arise from this if the upper layers are not hotplug-aware. This is
because the upper layers may still be holding references to the state of the device before
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Section 2.1, "Fibre Channel API".