Hello all,

In the process of building a new VM box to replace several individual CentOS servers, I've had the "interesting" experience of running both CentOS-5.5 and RHEL-6 (eval copy) as I build out the hardware based on a Supermicro motherboard.

A couple of observations regarding RAID-6:

- RAID-6 arrays created on RHEL-6 don't seem backward compatible with CentOS-5.5. This may or may not be expected behaviour, but it makes me wonder if forward compatibility might be a problem for those of us migrating large RAID-6 arrays from CentOS-5 to -6 systems. The main observations are that the md superblock is declared bad, and I get those boot-time messages claiming the available blocks are less than the configured size. As a result, the RAID arrays are not made available on CentOS-5.5.

- A total of 8 RAID-6 arrays in RHEL-6 are built with 2TB data disks plus a hot spare. However, every time I boot the system some, but not all, of the hot spare partitions are randomly missing. Using mdadm to manually add the spare partition back into an array always works. There are 4 array partitions per disk, and the largest single array is just over 2 TBytes of useable space. There are two groups of 5+1 drives spread across two SAS/SATA controller cards, and this random behaviour can occur on either one. Rebooting gets me a different set of missing hot spare partitions. The only error messages I get are the mdmonitor "missing spares event" emails ... nothing in dmesg.

The host OS has its own RAID-1 (+ hot spare) arrays on a separate set of disks and controller, and those arrays always come up correctly.

I've checked and double ckecked the mdadm.conf file to make sure the ARRAY, DEVICE and 'devices=....' statements are correct. Using mdadm to shut down an array and then reassemble it always seems to work properly, but something random is happening at boot-time assembly. It's only the hot spare partitions that don't appear, never the data partitions. Weird.

I'm hoping CentOS-6 doesn't present me with the same problem. Because I'm not a registered RHEL user, I don't have the ability to submit a bug report at RedHat.

Chuck