Managing I/O In Error Situations - Novell LINUX ENTERPRISE SERVER 11 - STORAGE ADMINISTRATION GUIDE 2-23-2010 Administration Manual

Whether the group is the first (highest priority) group
Paths contained within the group
The following information is displayed for each path:
The physical address as host:bus:target:lun, such as 1:0:1:2
Device node name, such as
Major:minor numbers
Status of the device

7.13 Managing I/O in Error Situations

You might need to configure multipathing to queue I/O if all paths fail concurrently by enabling
queue_if_no_path. Otherwise, I/O fails immediately if all paths are gone. In certain scenarios, where
the driver, the HBA, or the fabric experiences spurious errors, it is advisable that DM-MP be
configured to queue all I/O where those errors lead to a loss of all paths, and never propagate errors
upwards.
When using multipathed devices in a cluster, you might choose to disable queue_if_no_path. This
automaticall fails the path instead of queuing the I/O, and escalates the I/O error to causes a failover
of the cluster resources.
Because enabling queue_if_no_path leads to I/O being queued indefinitely unless a path is
reinstated, make sure that
might be stalled indefinitely on the affected multipathed device until reboot or until you manually
return to failover instead of queuing.
To test the scenario:
1 In a terminal console, log in as the
2 Activate queuing instead of failover for the device I/O by entering:
dmsetup message device_ID 0 queue_if_no_path
Replace the device_ID with the ID for your device. For example, enter:
dmsetup message 3600601607cf30e00184589a37a31d911 0 queue_if_no_path
3 Return to failover for the device I/O by entering:
dmsetup message device_ID 0 fail_if_no_path
This command immediately causes all queued I/O to fail.
Replace the device_ID with the ID for your device. For example, enter:
dmsetup message 3600601607cf30e00184589a37a31d911 0 fail_if_no_path
To set up queuing I/O for scenarios where all paths fail:
1 In a terminal console, log in as the
2 Open the
/etc/multipath.conf
3 Uncomment the defaults section and its ending bracket, then add the
setting, as follows:
defaults {
default_features "1 queue_if_no_path"
}
sda
is running and works for your scenario. Otherwise, I/O
multipathd
user.
root
user.
root
file in a text editor.
default_features
Managing Multipath I/O for Devices 75