Try this:
cat /proc/mdstat
result should be like this (obviously different in blocks)
md2 : active raid1 hda3[0] hdc3[1]
264960 blocks [2/2] [UU]
md1 : active raid1 hda2[0] hdc2[1]
7879808 blocks [2/2] [UU]
md0 : active raid1 hda1[0] hdc1[1]
104320 blocks [2/2] [UU]
the 2/2 and double UU means OK for mirrored partition partition
A,