I have a dedicated server at 1and1 with a software RAID. I believe it's running CentOS. The hardware team at 1and1 replaced the secondary hard drive (sdb) and then I followed these instructions to rebuild the array:
http://faq.1and1.com/dedicated_servers/root_server/linux_recovery/10.html
At step 9 I was not able to view mdadm.conf as it was a generic file without my configuration. I still continued on as I knew the array was built exactly as the instructions have laid out anyway.
I think this is a GRUB problem? Maybe I need to reconfigure mdadm.conf? I have no idea how to fix it. 1and1 allows me to boot into a recovery console which is pretty much just a live CD.
When I run cat /proc/mdstat
from the recovery console:
rescue:~# cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [faulty]
md1 : active raid1 sda1[0] sdb1[1]
3911680 blocks [2/2] [UU]
md3 : active raid1 sda3[1] sdb3[0]
482512192 blocks [2/2] [UU]
unused devices: <none>
Boot log from booting into recovery:
(Specifically I noticed this error: Assembling MD arrays...[31mfailed (no arrays found in config file or automatically) )