air hose the email server

Today I switched memory on the email server, Dell SC440. It went from 2GB to 4GB, the email server is actually inside a Xen DomU (guest). No head is on this machine. I knew it would not boot strait away with different memory size. On a Dell it tells you the memory size changed, do you want to continue or enter setup. I blindly hit F1 (continue). I did not known F1 was bypassing the warning that SATA2 was not found.

After fiddling around I found it had dropped /dev/sdb out of the RAIDs. Eeek. My dusting job with the air hose, was too invasive!

Not good:

# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [raid0] [raid1]
md2 : active raid5 sda4[0] sdd4[3] sdc4[2]
  444309504 blocks level 5, 256k chunk, algorithm 2 [4/3] [U_UU]

md0 : active raid1 sda1[0] sdc1[2]
  803236 blocks super 1.0 [3/2] [U_U]
  bitmap: 2/7 pages [8KB], 64KB chunk

md1 : active raid5 sda2[0] sdd2[3] sdc2[2]
  15710976 blocks level 5, 256k chunk, algorithm 2 [4/3] [U_UU]

So I needed to re-add it, but I can never remember the syntax. After some looking, this is what I did:

mdadm --misc --detail /dev/md0
mdadm --manage /dev/md0 --add /dev/sdb1
mdadm --misc --detail /dev/md1
mdadm --manage /dev/md1 --add /dev/sdb2
mdadm --misc --detail /dev/md2
mdadm --manage /dev/md2 --add /dev/sdb4