Chapter 7. Managing multipathed volumes

Procedure

1. Resize your physical device.

2. Find the paths to the logical unit number (LUN):

   # multipath -l

3. Resize your paths. For SCSI devices, writing a 1 to the rescan file for the device causes the SCSI driver to rescan, as in the following command:

   # echo 1 > /sys/block/path_device/device/rescan

   Ensure that you run this command for each of the path devices. For example, if your path devices are sda, sdb, sde, and sdf, run the following commands:

   # echo 1 > /sys/block/sda/device/rescan
   # echo 1 > /sys/block/sdb/device/rescan
   # echo 1 > /sys/block/sde/device/rescan
   # echo 1 > /sys/block/sdf/device/rescan

4. Resize your multipath device:

   # multipathd resize map multipath_device

5. Resize the file system, assuming no LVM or DOS partitions are used:

   # resize2fs /dev/mapper/mpatha

Procedure

1. Create the /etc/multipath.conf configuration file, load the multipath module, and set chkconfig for the multipathd to on:

   # mpathconf --enable

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 Preventing devices from multipathing.

3. Build a multipath device on top of the root device as soon as it is discovered. This command also ensures that find_multipaths allows the device, even if it only has one path.

   # multipath -a /dev/sdb`
   wwid '3600d02300069c9ce09d41c4ac9c53200' added

   Replace /dev/sdb with the root device name.

4. Confirm that your configuration file is set up correctly by executing 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 of 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. Rebuild the initramfs file system with multipath:

   # dracut --force -H --add multipath

6. Shut the machine down.
7. Boot the machine.
8. Make the other paths visible to the machine.

Procedure

1. Add the WWID of the device to the /etc/multipath/wwids file:

   # multipath -a /dev/sdb
   wwid '3600d02300069c9ce09d41c4ac9c53200' added

   Replace /dev/sdb with the swap device name.

2. Confirm that your configuration file is set up correctly by executing the multipath command and search the output for a line of the following format:

   date  wwid: ignoring map

   This indicates that the command failed to create the multipath device.

   For example, if the WWID of 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

3. Set up an alias for the swap device in the /etc/multipath.conf file:

   multipaths {
       multipath {
           wwid WWID_of_swap_device
           alias swapdev
       }
   }

4. Edit the /etc/fstab file and replace the old device path to the root device with the multipath device.

   For example, if you had the following entry in the /etc/fstab file:

   /dev/sdb2 swap                    swap    defaults        0 0

   Change the entry to the following:

   /dev/mapper/swapdev swap          swap    defaults        0 0

5. Rebuild the initramfs file system with multipath:

   # dracut --force -H --add multipath

6. Shut the machine down.
7. Boot the machine.
8. Make the other paths visible to the machine.