Chapter 7. Managing multipathed volumes

Procedure

1. Resize your physical device.

2. Execute the following command to 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, you would 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 enable the multipathd systemd service:

   # yum install device-mapper-multipath

2. 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

3. 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.

4. 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 allows 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

5. 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

6. Rebuild the initramfs file system with multipath:

   # dracut --force -H --add multipath

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

Procedure

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

   # multipath -a swap_devname

   For example, if the root device is /dev/sdb, enter the following command.

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

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.