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=====DM-Multipath in RHEL5=====

====Components====
^  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. |

====Installation and Configuration====
The basic procedure for configuring your system with DM-Multipath is as follows:
  - Install **device-mapper-multipath** rpm.
  - Edit the [[:linux:linux-san:dm-multipath-conf| dm-multipath.conf]] configuration file:
    - comment out the default blacklist
    - change any of the existing defaults as needed might want to enable either aliases or friendly names.
    - save the configuration file
  - Start the multipath [[:linux:linux-san:daemons|daemons]].
  - Create the multipath device with the [[:linux:linux-san:multipath|multipath]] command.