Novell LINUX ENTERPRISE SERVER 11 - STORAGE ADMINISTRATION GUIDE 2-23-2010, Administration Manual, Page: 75 / 140

Managing Multipath I/O for Devices 75
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Whether the group is the first (highest priority) group
Š
Paths contained within the group
The following information is displayed for each path:
Š
The physical address as host:bus:target:lun , such as 1:0:1:2
Š
Device node name, such as
sda
Š
Major:minor numbers
Š
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
multipathd
is running and works for your scenario. Otherwise, I/O
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
root
user.
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
root
user.
2 Open the
/etc/multipath.conf
file in a text editor.
3 Uncomment the defaults section and its ending bracket, then add the
default_features
setting, as follows:
defaults {
default_features "1 queue_if_no_path"
}