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Managing Multipath I/O for Devices 67
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Values are widely spaced because of the way the
multipath
command handles them. It multiplies
the number of paths in a group with the priority value for the group, then selects the group with the
highest result. For example, if a non-optimized path group has six paths (6 x 10 = 60) and the
optimized path group has a single path (1 x 50 = 50), the non-optimized group has the highest score,
so multipath chooses the non-optimized group. Traffic to the device uses all six paths in the group in
a round-robin fashion.
On failure, returns a value of 1 to 5 indicating the cause for the command’s failure. For information,
see the man page for
mpath_prio_alua
.
5.6.5 Reporting Target Path Groups
Use the SCSI Report Target Port Groups (
sg_rtpg(8)
) command. For information, see the man
page for
sg_rtpg(8)
.
5.7 Tuning the Failover for Specific Host Bus
Adapters
When using multipath I/O, you want any host bus adapter (HBA) failure or cable failures to be
reported faster than when multipathing is not in use. Configure time-out settings for your HBA to
disable failover at the HBA level to allow the failure to propogate up to the multipath I/O layer as
fast as possible where the I/O can be redirected to another, healthy path.
To disable the HBA handling of failover, modify the driver’s options in the
/etc/
modprobe.conf.local
file. Refer to the HBA vendor’s documentation for information about how
to disable failover settings for your driver.
For example, for the QLogic qla2xxx family of host bus adapters, the following setting is
recommended:
options qla2xxx qlport_down_retry=1
5.8 Configuring Multipath I/O for the Root Device
In the SUSE Linux Enterprise Server 10, the root partition (
/
) on multipath is supported only if the
/
boot
partition is on a separate, non-multipathed partition. Otherwise, no boot loader is written.
IMPORTANT: If you apply all online updates, the DM-MP is available but is not supported for
/
boot
and
/root
in SUSE Linux Enterprise Server 10 SP1 and later. More specifically, you need
mkinitrd
1.2-106.61 and
multipath-tools
0.4.7-34.23 or later. However, if you install the
packages and set up the configuration, you might run into update issues later.
Full multipath support is available in SUSE Linux Enterprise Server 11.
1 The device is in the standby group.
0 All other groups.
Priority Value Description