Novell LINUX ENTERPRISE SERVER 11 - STORAGE ADMINISTRATION GUIDE 2-23-2010, Руководство администратора, Страница: 69 / 140

Managing Multipath I/O for Devices 69
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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
.
7.6.5 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)
.
7.7 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 propagate 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
7.8 Configuring Multipath I/O for the Root Device
IMPORTANT: In the SUSE Linux Enterprise Server 10 SP1 initial release and earlier, 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.
DM-MP is now available and supported for
/boot
and
/root
in SUSE Linux Enterprise Server 11.
To enable multipathing on the existing root device:
1 Install Linux with only a single path active, preferably one where the
by-id
symlinks are listed
in the partitioner.
2 Mount the devices by using the
/dev/disk/by-id
path used during the install.
1 The device is in the standby group.
0 All other groups.
Priority Value Description