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DM-Multipath in RHEL5

Components	Description
dm-multipath kernel module	Reroutes I/O and supports failover for paths and path groups.
multipath command	Lists and configures multipath devices. Normally started up with /etc/rc.sysinit, it can also be started up by a udev program whenever a block device is added or it can be run by the initramfs file system.
multipathd daemon	Monitors paths; as paths fail and come back, it may initiate path group switches. Provides for interactive changes to multipath devices. This must be restarted for any changes to the /etc/multipath.conf file.
kpartx command	Creates device mapper devices for the partitions on a device It is necessary to use this command for DOS-based partitions with DM-MP. The kpartx is provided in its own package, but the device-mapper-multipath package depends on it.

The basic procedure for configuring your system with DM-Multipath is as follows:

Install device-mapper-multipath rpm.
Edit the dm-multipath.conf configuration file:
1. comment out the default blacklist
2. change any of the existing defaults as needed might want to enable either aliases or friendly names.
3. save the configuration file
Start the multipath daemons.
Create the multipath device with the multipath command.