Re: Corrupted persistent superblock - repairable?
From: Enrique Perez-Terron (enrio_at_online.no)
Date: Wed, 19 Oct 2005 00:01:08 +0200
On Tue, 18 Oct 2005 16:37:20 +0200, Rohan Beckles <firstname.lastname@example.org> wrote:
> Hello --
> Recent failures of successive system disks (30 days apart!) convinced me to
> employ two RAID Edition HDs as system disks, in a RAID 1 configuration.
> The partitions on these disks are referred to in /etc/raidtab as /dev/md0
> (/boot, mirrored) and /dev/md1 (/, mirrored).
> Before my recent system upgrade, my two-drive RAID0 array (2 Western Digital
> Caviar 250GB HDs, for music and stuff) was configured as /dev/md0. My
> RAID0 array is now referred to in /etc/raidtab as /dev/md2. Now,
> post-upgrade, this array cannot be mounted on startup.
> /sbin/raidstart complains that both copies of the persistent superblock are
> corrupt. The array can only be started manually now, using /sbin/raid0run,
> after booting.
> I suspect that the root reason is that the superblock on this array has
> "/dev/md0" (and the drives that are associated with it) written in it, and
> of course /dev/md0 is now claimed by other devices.
> Is there anyway to updated the superblock of my RAID0 array to reflect its
> new device node name, i.e. "/dev/md2"? It would be even better if I could
> do this without destroying any data on the disk.
You could use mdadm:
# mdadm --examine /dev/hda1
Magic : a92b4efc
Version : 00.90.02
UUID : f0e9e745:51c48643:e1d520af:00422121
Creation Time : Fri Oct 7 15:07:16 2005
Raid Level : raid1
Raid Devices : 2
Total Devices : 2
Preferred Minor : 0
Update Time : Sun Oct 9 16:18:40 2005
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Checksum : 5481f27b - correct
Events : 0.108
Number Major Minor RaidDevice State
this 1 3 1 1 active sync /dev/hda1
0 0 3 65 0 active sync /dev/hdb1
1 1 3 1 1 active sync /dev/hda1
Look specifically at the line "Raid Level", to see if it is now a raid1 or raid0.
Check what other devices belong to the same volume (bottom).
mdadm --zero-superblock --force /dev/hda1
mdadm --zero-superblock --force /dev/hdb1
mdadm --create /dev/md0 --level=raid1 --raid-devices=2 /dev/hda1 /dev/hdb1
1. I have minimal experience with mdadm and md devices. The commands may not
even be correct as shown.
2. Ensure that the *file system* on the devices is smaller than
the partition size, by enough to allow for an md superblock.
echo "($(fdisk -s /dev/hda1)/64 - 1)*64" | bc
should tell the usable size of /dev/hda1. Use the smallest number from
all component devices. Check that the actual file system size is less
than or equal to that.
3. When creating an md device, the first component becomes the
master copy, and the other component(s) are overwritten to
make them equal.