[Gllug] RAID superblock on /dev/sda2 appearing on /dev/sda

[John Edwards]

Hi

I've got a very strange problem at the moment.

New Supermicro server, SATA dmRAID disabled, two 500GB SATA drives
partitioned as 20GB (/dev/sd[a-b]1) and 480GB (/dev/sd[a-b]2).

The two 20GB partitions are an mdadm RAID1 for an ext3 root
filesystem and work fine.

The two 480GB partitions are an mdadm RAID1 for an LVM physical
volume which work fine during the install of Ubuntu 10.04.1 but
not after the machines reboots. After the reboot it thinks that
/dev/sda and /dev/sdb (eg whole disks) are part of a RAID array
and that /dev/sda1 and /dev/sdb1 are partitions of that RAID
(eg /dev/md1_p1).

The weird thing is that when I zero the RAID superblocks for
/dev/sda and /dev/sdb it also zeroes the superblocks on the
/dev/sda2 and /dev/sdb2 partitions.

When I recreate the RAID on the partitions (/dev/sda2 and
/dev/sdb2) I get the same superblock created on /dev/sda
and /dev/sdb. The command I used was:
	mdadm --create --level=1 -n 2 /dev/md1 /dev/sda2 /dev/sdb2

I've tried zero'ing both the disks using dd, and switched between
AHCI and IDE mode in the BIOS.


A previous server of the same type was installed last month, but
does not show the same problems. The main difference with that 
server was that 2nd RAID array with LVM was setup after the install
had finished.

Reading the mdadm RAID superblock docs:
	https://raid.wiki.kernel.org/index.php/RAID_superblock_formats

It appears that the current 0.90 superblocks are written towards
the end of the device. Could it be possible that the end of the
partition of very close to the end of the disk and so the two
are getting confused?

Any other ideas on what is going on?


-- 
#---------------------------------------------------------#
|    John Edwards   Email: john at cornerstonelinux.co.uk    |
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