From: =?UTF-8?Q?Krzysztof_Kosi=C5=84ski?= <tweenk.pl@gmail.com>
Subject: Massive corruption on RAID0
Date: Mon, 29 Jun 2009 02:38:10 +0200
Message-ID: <298610bb0906281738u2e1ce91fnc753acc145d759bb@mail.gmail.com>
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To: linux-ext4@vger.kernel.org
Sender: linux-ext4-owner@vger.kernel.org

Hello

Here is my story: I recently migrated a server from Windows to Ubuntu
9.04. I formatted all disks with ext4. The server has 5 disks: three
SCSI (9GB for /, 2x18GB for /data/small and /home) and two IDE
(2x300GB). I put the IDE disks in a RAID0: each had a single partition
with type set to "fd", and the entire resulting device (/dev/md0) was
formatted with ext4 as:

mkfs.ext4 -b 4096 -E stride=3D16 /dev/md0

All was well until a power outage that left the filesystem on /dev/md0
unmountable (the others were fine after an fsck). I made a backup of
the corrupted array to another disk and ran fsck, but it ended up in
an infinite loop. After some unsuccessful tinkering, I restored the
backup and found out that large portions of the group descriptor table
are filled with random junk. Moreover, all backup superblocks are
either corrupted or zeroed, and I found partial copies of an
identically corrupted table at various weird offsets (including
176888, 600344, 1036536, 1462520, 1887256 and 5326832); neither of
these copies were preceded by anything resembling a superblock. Here
is a copy of first 39 blocks of the corrupted disk:
http://tweenk.artfx.pl/super.bin

The group descriptors that are not filled with random junk all follow
a simple pattern, but filling the group descriptor table with with an
extension of it didn't yield anything interesting. A smartctl check
revealed that one of the disks forming the array has
Reallocated_Sector_Ct =3D 17 and Reallocated_Event_Count =3D 1
(coincidentally, 17 is also the number of backup superblocks this
device should have), the other has zero; however, this doesn't explain
the massive corruption.

Regards, Krzysztof Kosi=C5=84ski

PS Please CC replies to me as I'm not subscribed
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