HP Serviceguard Extended Distance Cluster for Linux A.11.20.10 Deployment Guide, December 2012

Example 4 Adding a new disk as an MD component to /dev/md0 array
To add a new disk to the/dev/md0 array, run the following command:
# mdadm - -add /dev/md0 /dev/hpdev/sde
Following is an example of the status message displayed in the /proc/mdstat file once the disk
is added:
Personalities : [raid1]
md0 : active raid1 sde[2] sdf[0]
9766784 blocks [2/1] [U_]
[=>...................] recovery = 8.9% (871232/9766784) finish=2.7min
speed=54452K/sec
unused devices: <none>
48 Managing an MD Device