You can simply view /proc/mdstat:
cat /proc/mdstat
Example output
Personalities : [raid1] [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid10]
md2 : active raid5 sdb3[4] sdd3[0] sda3[2] sdc3[1]
2111434752 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UUU_]
[===>.................] recovery = 16.2% (114244316/703811584) finish=48.8min speed=201053K/sec
bitmap: 2/6 pages [8KB], 65536KB chunk
md1 : active raid1 sdb2[3] sda2[2] sdd2[0] sdc2[1]
1046528 blocks super 1.2 [4/4] [UUUU]
md3 : active raid5 sdb4[4] sda4[2] sdd4[0] sdc4[1]
44661594624 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UUU_]
resync=DELAYED
bitmap: 2/111 pages [8KB], 65536KB chunk
md0 : active raid1 sda1[2] sdb1[3] sdd1[0] sdc1[1]
33520640 blocks super 1.2 [4/4] [UUUU]
unused devices: <none>