I'm running CentOS 5.5, the system, boot, swap, etc. is all on /dev/sda and I have two identical single-partition drives /dev/sdb1 /dev/sdc1 that are configured in RAID1 (using mdadm). It was working fine (configured to mount to /mnt/data in the fstab file) and I recently let yum install a couple of automatic updates without paying attention to what they were, and now it doesn't work.

Raid is working fine (dmesg shows it gets loaded correctly). mdstat shows:

# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdc1[1] sdb1[0]
      XXXX blocks [2/2] [UU]

unused devices: <none>

Additionally, I can mount it anywhere other than its default directory (i.e. the following works, and I can read data off the drives).

# mount /dev/md0 /mnt/data2
EXT3-fs warning: mounting fs with errors, running e2fsck is recommended

But when I run the following I get:

# mount -a
mount: /dev/sdb1 already mounted or /mnt/data busy

It says nothing is mounted when I try to umount /dev/sdb1 or umount /mnt/data, so I assume it's the second of those errors. However, lsof | grep mnt shows nothing. The weird thing is that I can save files in /mnt/data. So something is obviously mounted there, but when I try to umount it I get the error that nothing is mounted. /etc/mtab doesn't mention any of the partitions or files I am trying to work with, and fstab just has that one line I mentioned above that is supposed to mount my raid partition. Again, it was all working fine until I

On Google I've found a few things about dmraid interfering with mdadm after an update, but I yum remove'd dmraid and rebooted and it didn't help.

I'm really confused and need to get this working to get on with my work!