I just upgraded my home KVM server to CentOS 6.0 CR to make use of the latest libvirt and now my RAID array with my VM storage is missing. It seems that the upgrade to mdadm-3.2.2 is the culprit.
This is the output from mdadm when scanning that array,
# mdadm --detail --scan ARRAY /dev/md0 metadata=imsm UUID=734f79cf:22200a5a:73be2b52:3388006b ARRAY /dev/md126 metadata=imsm UUID=3d135942:f0fad0b0:33255f78:29c3f50a mdadm(IMSM): Unsupported attributes : 40000000 mdadm: IMSM metadata loading not allowed due to attributes incompatibility. mdadm(IMSM): Unsupported attributes : 40000000 mdadm: IMSM metadata loading not allowed due to attributes incompatibility. ARRAY /dev/md127 container=/dev/md0 member=0 UUID=734f79cf:22200a5a:73be2b52:3388006b
The error about IMSM shows up on google as something that happened to Fedora users during a FC14->FC15 upgrade.
The server itself isn't old, it's a Supermicro 2U with Dual Xeon 5400 family of CPU. There are two RAIDs on this one controller...a RAID1 which still functions and a RAID5 which is the one that is unable to be seen. I don't know what IMSM is for, but the only thing strange about that array is it is 2.7TB so the BIOS configured it as two separate arrays, one as 2TB and one as 700GB, but it was showing up to CentOS as a single volume.
I downgraded to 3.2.1 , ran mdadm again and bam...it works,
# mdadm --detail --scan ARRAY /dev/md0 metadata=imsm UUID=734f79cf:22200a5a:73be2b52:3388006b ARRAY /dev/md126 metadata=imsm UUID=3d135942:f0fad0b0:33255f78:29c3f50a ARRAY /dev/md127 container=/dev/md0 member=0 UUID=691f975d:6beecfd8:67b39886:b7ee7f6e
Hopefully this can be fixed before this version makes it to 6.1, though it's likely a problem for upstream RHEL as well.
- Trey