Re: Problem converting raid-5 array from 2.2.17 into 2.4.22

Problem solved!

Using mdadm, I discovered that the superblock's checksum was supposed to
be something else, but it was - zero! So, I wondered, what the heck, maybe
if I'd use some hex editor and change the actual checksum to be what it
expects... and turns out that it worked!

So it appears that there is a bug in "mkraid --upgrade" that leaves the checksum
being zero, while it should (re)calculate the checksum and set it to its correct
value after upgrading. I used the raidtools version 0.90.x which comes with debian
stable, though; I don't know it the problem exists if you upgrade with raidtools
1.00.x. I can provide details if someone is interested.

If someone else has experienced this, I recommend lde (linux disk editor) for editing
the raid root block. Block numbers I found from an old syslog (where it says that
raid disk cannot be due to invalid superblock checksum)

Phew!

-J

From: "John Doe" <redacted>
To: <redacted>
Subject: Re: Problem converting raid-5 array from 2.2.17 into 2.4.22
Date: Wed, 03 Sep 2003 16:47:14 +0300

quoted

# mdtab entry for /dev/md0
/dev/md0        raid5,128k,0,93fa4522   /dev/hda3 /dev/hdb1 /dev/hdc1 /dev/hdd1

# /etc/raidtab:
raiddev /dev/md0
       raid-level      5
       nr-raid-disks   4
       nr-spare-disks  0
       persistent-superblock   1
       parity-algorithm        left-symmetric
       chunk-size      32

[...]

quoted

This one was copied straight from Software-RAID HOWTO, unfortunately I noticed only afterwards that the chunk-size was different than it was before.

I also reproduced the situation on a different machine and different disks,
with this time the right chunk-size (128 kb). And it didn't work either!

So it seems that "mkraid --upgrade" will *always* break a raid5 setup, at least
if it's me doing the conversion :)

This sounds pretty alarming.

I hope there is some way to reconstruct the superblocks or change their
checksums or something. Next I'm going to spend a few hours investigating if
mdadm and newer raidtools have options for doing this.

-J

_________________________________________________________________
Get MSN 8 and help protect your children with advanced parental controls.  http://join.msn.com/?page=features/parental

-
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

_________________________________________________________________
Get MSN 8 and enjoy automatic e-mail virus protection.    http://join.msn.com/?page=features/virus