Check status of md devices

cat /proc/mdstat

In the example below, 'md0' is synchronizing replicas, 'md1' and 'md2' are not synchronized and 'md3' is fully replicated.

root# cat /proc/mdstat
Personalities : [raid0] [raid1]
read_ahead 1024 sectors
md3 : active raid0 hdb6[1] hda6[0]
227962112 blocks 32k chunks

md2 : active raid1 hda5[0] hdb5[1]
14578880 blocks [2/2] [UU]
resync=DELAYED
md1 : active raid1 hda3[0] hdb3[1]
14578880 blocks [2/2] [UU]
resync=DELAYED
md0 : active raid1 hda1[0] hdb1[1]
9759360 blocks [2/2] [UU]
[============>........] resync = 62.5% (6107456/9759360) finish=38.7min speed=1568K/sec
unused devices: <none>