#Stop mdadm
mdadm -S /dev/md0

#clean partition
mdadm --zero-superblock /dev/sdb1

---------------------
cat /proc/mdstat
md10 : active(auto-read-only) raid1 sdc1[0] sdd1[1]
390708736 blocks [2/2] [UU]
resync=PENDING

apparently auto-read-only prevents the array from being rebuilt; it's
been pending for hours.

Solution: Try:
mdadm --readwrite /dev/md10


===================================

#REMOVE/DESTRO/DELETE raid
# /dev/md1 = raid5 of 4 drives

root@rtr-1:~# mdadm -S /dev/md1
mdadm: stopped /dev/md1
root@rtr-1:~# mdadm --zero-superblock /dev/sda2
root@rtr-1:~# mdadm --zero-superblock /dev/sdb2
root@rtr-1:~# mdadm --zero-superblock /dev/sdc2
root@rtr-1:~# mdadm --zero-superblock /dev/sdd2
root@rtr-1:~# sync
root@rtr-1:~# reboot

--------------------------------------


mdadm --create md-device --chunk=X --level=Y --raid-devices=Z devices
------------------

http://www.howtoforge.com/how-to-resize-raid-partitions-shrink-and-grow-software-raid

---------------------------------

mdadm -Asv


mdadm -E /dev/sd[abcd]2|less


mdadm --examine --scan --config=mdadm.conf >> /etc/mdadm/mdadm.conf

-----------------------------------

after upgrade software raid array wouldn't start
do did a NEW create:

root@filer2:~# mdadm --create /dev/md0 --verbose --level=5 --raid-devices=4 /dev/sd[abcd]2
mdadm: layout defaults to left-symmetric
mdadm: chunk size defaults to 512K
mdadm: layout defaults to left-symmetric
mdadm: layout defaults to left-symmetric
mdadm: layout defaults to left-symmetric
mdadm: /dev/sdb2 appears to be part of a raid array:
    level=raid5 devices=4 ctime=Tue Jul 19 16:56:10 2011
mdadm: layout defaults to left-symmetric
mdadm: /dev/sdc2 appears to be part of a raid array:
    level=raid5 devices=4 ctime=Tue Jul 19 16:56:10 2011
mdadm: layout defaults to left-symmetric
mdadm: /dev/sdd2 appears to be part of a raid array:
    level=raid5 devices=4 ctime=Tue Jul 19 16:56:10 2011
mdadm: size set to 972566016K
Continue creating array? (y/n) y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
root@filer2:~# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdd2[4] sdc2[2] sdb2[1] sda2[0]
      2917698048 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UUU_]
      [>....................]  recovery =  0.0% (153824/972566016) finish=316.0min speed=51274K/sec

unused devices: <none>