From: Ville Herva <vherva@niksula.hut.fi>
To: linux-kernel@vger.kernel.org
Cc: Willy Tarreau <willy@w.ods.org>
Subject: Re: Something corrupts raid5 disks slightly during reboot
Date: Fri, 2 Jan 2004 21:42:00 +0200 [thread overview]
Message-ID: <20040102194200.GA11115091@niksula.cs.hut.fi> (raw)
In-Reply-To: <20031101190114.GA936@alpha.home.local>
Summary:
I've been experiencing strange corruption on a raid5 volume for some time.
The kernel is 2.2.x + RAID-0.90 patch. Fs is ext2 (+e2compr). After
unmounting the filesystem, I can mount it again without problems. I can also
raidstop the raid device in between and all is still fine:
> umount /dev/md4; mount /dev/md4
- no corruption
> umount /dev/md4; raidstop /dev/md4; raidstart /dev/md4; mount /dev/md4
- no corruption
But after a reboot, the filesystem is corrupted - few bytes differ in the
beginning of /dev/md4 between 1k and and 5k.
See the threads
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=utf-8&threadm=MMYt.4B2.1%40gated-at.bofh.it&rnum=1&prev=/groups%3Fnum%3D50%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3Dutf-8%26q%3DSomething%2Bcorrupts%2Braid5%2Bdisks%2Bslightly%2Bduring%2Breboot%26sa%3DN%26tab%3Dwg
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=utf-8&threadm=MZsH.72R.5%40gated-at.bofh.it&rnum=4&prev=/groups%3Fnum%3D50%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3Dutf-8%26q%3DSomething%2Bcorrupts%2Braid5%2Bdisks%2Bslightly%2Bduring%2Breboot%26sa%3DN%26tab%3Dwg
for details.
I did some futher research.
First I thought this was an artifact of using "non-normal" blocksize on the
fs, 4096 bytes. The other raid partitions I have on the system are 1024 and
do not get corrupted.). Also the corrupting fs is on raid5 on bare disks
(hdb+hdc+hdg), while the others are on partitions (hda1+hdd1+hdf1 and so
on.)
I tried to reproduce this under vmware with 3-disk raid5 (hda+hdb+hdd) using
4096-byte ext2 and the exact same kernel. Initially, I thought I was able to
trigger it by mounting the fs while raid rebuild was on progress. The kernel
spitted this:
set_blocksize: b_count 1, dev md(9,4), block 15642112, from c014c3fb
set_blocksize: b_count 1, dev md(9,4), block 15642113, from c014c3fb
set_blocksize: b_count 1, dev md(9,4), block 15642114, from c014c3fb
...
set_blocksize: b_count 2, dev md(9,4), block 15642367, from c014c3fb
md4: blocksize changed during read
nr_blocks changed to 64 (blocksize 4096, j 3910528, max_blocks 39091968)
and fsck reported problems, but only once (the set_blocksize stuff appeared
each time). It seems the "set_blocksize" outpouring is a known issue, and
not severe:
http://www.ussg.iu.edu/hypermail/linux/kernel/0110.1/0493.html
The fsck errors were probably just a side-effect of unclean shutdown I used
to force raid rebuild.
After the failed vmware experiment, I tried to isolate when exactly the
corruption happens, shutdown or boot. Also, in the mentioned threads, people
had suggested turning off the write cache of the IDE disk.
I found out that the difference (corruption) is usually on three bytes on
/dev/hdg, but sometimes on /dev/hdc, too. (/dev/md4 = hdb+hdc+hdg; hdb&hdc
are on i810, hdg is on hpt370).
First, I did
umount /dev/md4
raidstop /dev/md4
head -c 50k /dev/hdg > /save/hdg
reboot
To rule out kernel raid autodetect and raid code in general, I
booted 2.2.25-1-secure with "single init=/bin/bash raid=noautodetect".
Did
head -c50k /dev/hdg | cmp -l /save/hdg
Three bytes differed:
4641 0 35
4642 0 205
4643 0 10
bytepos after before
boot boot
wrote the original stuff back:
dd if=/save/hdg /dev/hdg
sync
hdparm -W0 /dev/hdg
sync
reboot
Booted 2.2.25-1-secure with "single init=/bin/bash raid=noautodetect"
again.
Did
head -c50k /dev/hdg | cmp -l /save/hdg
Three same three bytes differed again.
Wrote the stuff back, sync'ed, did hdparm, and powered off. Still, the the
bytes differed on next boot.
Then I booted 2.4.21-jam1 with "single init=/bin/bash raid=noautodetect" (I
happened to have 2.4.21-jam1 compiled with suitable drivers at hand).
Wrote the same stuff back with dd, synced, turned ide cache off.
Booted 2.4.21-jam1 with "single init=/bin/bash raid=noautodetect" again.
Did the diff; the three bytes differed again.
Note that sometimes few bytes on hdc differed, too. Usually it was just the
three hdg bytes.
So this is not a 2.2 kernel issue. I very much doubt it's a kernel issue at
all. Unless it is a bug in kernel partition detection that is still present
in 2.4.x.
I tried to turn off the ide write cache with hdparm -W0, so it shouldn't
be a write caching issue.
If it's a bios issue, it's really a strange one, since it affects both disks
on i810 ide and on hpt370. The disks have no partition table, though, which
_could_ confuse the bios.
Any ideas? Who the heck could write to those three bytes, and why?
-- v --
v@iki.fi
next prev parent reply other threads:[~2004-01-02 19:42 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-31 19:08 Something corrupts raid5 disks slightly during reboot Ville Herva
2003-11-01 1:41 ` Jeffrey E. Hundstad
2003-11-01 1:57 ` Mike Fedyk
2003-11-01 8:33 ` Ville Herva
2003-11-01 8:27 ` ide write cache issue? [Re: Something corrupts raid5 disks slightly during reboot] Ville Herva
2003-11-01 15:56 ` Willy Tarreau
2003-11-01 18:25 ` Ville Herva
2003-11-01 19:01 ` Willy Tarreau
2003-11-01 21:02 ` Ville Herva
2003-11-02 6:05 ` Andre Hedrick
2003-11-02 8:28 ` Ville Herva
2003-11-02 20:57 ` Matthias Andree
2003-11-03 5:34 ` Andre Hedrick
2003-11-03 6:38 ` Ville Herva
2004-01-02 19:42 ` Ville Herva [this message]
2004-01-02 20:02 ` Something corrupts raid5 disks slightly during reboot Ville Herva
2004-01-14 14:46 ` Ville Herva
2004-01-14 22:22 ` Willy Tarreau
2004-01-14 22:46 ` Ville Herva
2004-01-14 16:39 Samium Gromoff
2004-01-14 22:30 ` Ville Herva
2004-01-15 12:42 ` Samium Gromoff
2004-01-15 19:57 ` Ville Herva
2004-01-16 10:24 ` Samium Gromoff
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