How to Adding and Failing RAID Partitions

To add a partition to a RAID device, execute the following as root after creating the partition of type Linux raid auto (fd in fdisk):

mdadm /dev/mdX -a <device list>

To add /dev/sda8 to the /dev/md0 RAID device created in the previous section:

mdadm /dev/md0 -a /dev/sda8

shows the output from cat /proc/mdstat. The /dev/sda8 partition is now a spare partition in the RAID array.

Adding a Spare Partition

Personalities : [raid0] [raid1]

md0 : active raid1 sda8[3](S) sda7[2] sda6[1] sda5[0]

10241280 blocks [3/3] [UUU]

[>....................] resync = 0.6% (66560/10241280) finish=84.0min

speed=2016K/sec

unused devices: <none>

If a partition in the array fails, use the following to remove it from the array and rebuild the array using the spare partition already added:

mdadm /dev/mdX -f <failed device>

For example, to fail /dev/sda5 from /dev/md0 and replace it with the spare (assuming the

spare has already been added):

mdadm /dev/md0 -f /dev/sda5

To verify that the device has been failed and that the rebuild has been complete and was successful, monitor the /proc/mdstat file.

tail -f /proc/mdstat

Notice that /dev/sda5 is now failed and that /dev/sda8 has changed from a spare to an active partition in the RAID array.

Failing a Partition and Replacing with a Spare

Personalities : [raid0] [raid1]

md0 : active raid1 sda8[3] sda7[2] sda6[1] sda5[4](F)

10241280 blocks [3/2] [_UU]

[>....................] recovery = 0.2% (30528/10241280) finish=11.1min

speed=15264K/sec

unused devices: <none>