Installation guide

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Appendix C. Multipath-usage.txt File for Red Hat Enterprise Linux 4
Update 3
priority path group. Other options for multipathd are to (a) wait
for a user-defined length of time (for the path groups to stabilize)
and then switch or (b) for multipathd to do nothing and wait for
manual intervention. Failback can be forced at any time by
running the multipath command.
Multipath device:
The multipath device is the device mapper device created by
dm-multipath. A multipath device can be identified by either
its WWID or its alias. A multipath device has one or more path
groups. It also has numerous attributes defined in the
following file:
/usr/share/doc/device-mapper-multipathd-0.4.5/multipath.conf.annotated
alias:
The alias is the name of a multipath device. By default, the
alias is set to the WWID. However, by setting the
"user_friendly_names" configuration option, the alias is set to a
unique name of the form mpath<n>. The alias name can also be
explicitly set for each multipath device in the configuration file.
NOTE: While the alias in guaranteed to be unique on a node, it
is not guaranteed to be the same on all nodes using the
multipath device. Also, it may change.
WWID:
The WWID (World Wide Identifier) is an identifier for the
multipath device that is guaranteed to be globally unique and
unchanging. It is determined by the getuid callout program.
Using DM-MP
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Initial setup:
1. If it is not already installed. Install the device-mapper-multipath
package.
2. Edit /etc/multipath.conf. For new installations, all devices are
blacklisted. The default blacklist is listed in the commented out
section of /etc/multipath.conf. If you comment out or delete
the following lines in /etc/multipath.conf, the default blacklist
takes effect:
devnode_blacklist {
devnode "*"
}