[OT] Re: Corrupt bazaar repositories
Martin at lichtvoll.de
Fri Jun 22 18:34:22 BST 2007
Am Freitag 22 Juni 2007 schrieb David Cournapeau:
> Martin Steigerwald wrote:
> > Hello!
> > I have quite some corrupt Bazaar repositories after I tried out
> > xfs_fsr - the online defragmentation tool for XFS. I had something
> > similar with KMail index files and a Mercurial repository. I dunno
> > whether it is related to xfs_fsr or not. At least I could not
> > reproduce this up to now - neither with KMail indexes nor with a bzr
> > repository, but aside from the broken ones I had no Bazaar repository
> > with fragmented files.
> I know this won't solve your problem, but using XFS on PC-quality
> hardware really is a bad idea, this has been mentioned many times by
> knowledgable people, see for example .
>  http://linuxmafia.com/faq/Filesystems/reiserfs.html
Well I know XFS quite deeply from first hand experience and since a quite
long time. And since 18.104.22.168 it has been really stable. Before that
there could have been crashes when write caches were enabled cause write
barriers were not supported / enabled by default. Thats a problem that
other journaling filesystem face too, may be that XFS is a bit more
vulnerable to it, but technically spoken any journalling filesystem needs
some write ordering in order to prevent corruption on abnormal write
termination. See the XFS FAQ or my article for details. Other
filesystems like ext3, ReiserFS3, Reiser4 also have write barrier support
for exactly that reason.
I use XFS on two ThinkPads and we use it on 10 Dell workstations in the
company and we also use it on some servers. And its just stable since
22.214.171.124 or before, too, *when* write caches were disabled - even 2.6.16
were I had the most problems with enabled write caches was stable with
disabled write cache. 126.96.36.199 and 188.8.131.52 had a slight directory
corruption bug, that is fixable by a current xfs_repair, also mentioned
in the FAQ.
From all I seen on the XFS mailing list, the XFS people respond quickly to
any corruption issues reported. Other filesystems are not free from
corruption issues as well, just search "ext3 corruption" or "ext3
corruption 2007" on Google to get an idea. Likewise for ReiserFS3, Reiser
4 and JFS.
Just to spread some up-to-date information on this topic.
I can not yet prove / reproduce it, but it seemed that xfs_fsr - the
online defragmentation tool for XFS - corrupted some files. I found those
corrupted Bazaar and Mercurial repos as well as KMail index files shortly
after I can xfs_fsr. I had no meta data corruption on XFS itself at all.
Actually I didn't really need to use xfs_fsr since the filesystems were
not badly fragmented at all. I just liked to try it out. It does not seem
that many people use it. But granted if it really is xfs_fsr that
corrupted the files this is bad. I informed the XFS people already about
the problem and if I can reproduce it I will file a bug report about it -
maybe even if not.
It seems to be typical file content corruption - file content changed, but
date as well as size remained the same. I was in luck, cause rsync didn't
copy those corrupted repositories to my backup drive exactly for that
reason, except for the Bazaar article repo, which was one of the last
articles I worked on.
Thus fixing my bazaar article repository would mean to correct those
corrupted bytes... well maybe I can see a pattern, when "comparing" a
good and a broken repository with rsync -ac ;-). This should give me the
broken files and then I can cmp them.
 Published in issue http://www.linux-magazine.com/issue/78 (SysAdmin:
Write Barrier). Not yet available online.
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA B82F 991B EAAC A599 84C7
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