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5.3. Moving root File Systems from a Single Path Device to a Multipath Device

If you have installed your system on a single-path device and later add another path to the root file system, you will need to move your root file system to a multipathed device. This section documents the procedure for moving from a single-path to a multipathed device.
After ensuring that you have installed the device-mapper-multipath package, perform the following procedure:
  1. Execute the following command to create the /etc/multipath.conf configuration file, load the multipath module, and set chkconfig for the multipathd to on: 
    # mpathconf --enable
    For further information on using the mpathconf command to set up multipathing, see Section 3.1, “Setting Up DM Multipath”.
  2. If the find_multipaths configuration parameter is not set to yes, edit the blacklist and blacklist_exceptions sections of the /etc/multipath.conf file, as described in Section 4.2, “Configuration File Blacklist”.
  3. In order for multipath to build a multipath device on top of the root device as soon as it is discovered, enter the following command. This command also ensures that find_multipaths will allow the device, even if it only has one path. 
    # multipath -a root_devname
    For example, if the root device is /dev/sdb, enter the following command. 
    # multipath -a /dev/sdb
wwid '3600d02300069c9ce09d41c4ac9c53200' added
  4. To confirm that your configuration file is set up correctly, you can enter the multipath command and search the output for a line of the following format. This indicates that the command failed to create the multipath device. 
    date  wwid: ignoring map
    For example, if the WWID if the device is 3600d02300069c9ce09d41c4ac9c53200, you would see a line in the output such as the following: 
    # multipath
Oct 21 09:37:19 | 3600d02300069c9ce09d41c4ac9c53200: ignoring map
  5. To rebuild the initramfs file system with multipath, execute the dracut command with the following options: 
    # dracut --force -H --add multipath
  6. Shut the machine down.
  7. Configure the FC switch so that other paths are visible to the machine.
  8. Boot the machine.
  9. Check whether the root file system ('/') is on the multipathed device.
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