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

"John Doe" <public_address_911@hotmail.com> · Wed, 03 Sep 2003 18:47:44 +0300

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" <public_address_911@hotmail.com>
To: linux-raid@vger.kernel.org
Subject: Re: Problem converting raid-5 array from 2.2.17 into 2.4.22
Date: Wed, 03 Sep 2003 16:47:14 +0300

# 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
[...]
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

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