Md0 : active (auto-read-only) in /proc/mdadm
Ever seen this message in your /proc/mdstat right after you boot the server and wondered what it is?
# cat /proc/mdstat Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md2 : active raid1 sda3 sdb3 1458830400 blocks [2/2] [UU] md1 : active raid1 sda2 sdb2 2104448 blocks [2/2] [UU] md0 : active (auto-read-only) raid1 sda1 sdb1 4200896 blocks [2/2] [UU] unused devices: <none>
Your array is not broken - it simply means nothing was yet written to that array (unless you were changing anything with --readonly option to mdadm).
I.e. if a mounted filesystem is on a given device, you are unlikely to see this. On a swap device, however, you may see it.
Assuming the device is /dev/md0 and is used for swap, do a:
# swapoff /dev/md0 # mkswap /dev/md0 # swapon /dev/md0
and you will see “auto-read-only” is gone (careful, if you use UUIDs).