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Re: XFS and XEN

To: xfs@xxxxxxxxxxx
Subject: Re: XFS and XEN
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Tue, 24 Feb 2009 16:04:24 +0100
In-reply-to: <200902170959.55077@xxxxxx>
Organization: it-management http://it-management.at
References: <200902170959.55077@xxxxxx>
User-agent: KMail/1.10.3 (Linux/; KDE/4.1.3; x86_64; ; )
On Dienstag 17 Februar 2009 Michael Monnerie wrote:
> Now I'm sure that the following configuration can destroy a
> PostgreSQL 8.3.5 database:
> * Linux host with XEN, XFS filesystem with "nobarrier", RAID
> controller with battery backed cache.
> * XEN vm with XFS filesystem with "nobarrier" with postgresql
> * your daughter with 3.5 years switching off the power supply of the
> server

I got this answer on the XEN list. It looks like XFS in not very secure. 
Do you share that opinion? I am still searching for a way to make sure 
the above never happens again. Should I use ext3/reiserfs/ocfs2 within a 
XEN domU, or is it not the fault of XFS my database got destroyed? Don't 
want to blame anyone, but I need a secure environment for the machines 
that should be in production soon, don't have time to recover databases 
or whatever just because of a crash.

from XEN list:
if you don't have highly reliable hardware, with redundant channels and 
battery backed caches, etc. stay away from XFS.

it's a pity, but XFS is only as reliable as the hardware you give it.  
in other words: you can be really sure that a software issue won't trash 
your XFS filesystem; but also that a hardware failure definitely will.

ext3, OTOH, might not have such an impressive record of correctness; but 
it's designed with redundancy in mind.  almost all vital structures are 
either replicated or reconstructable from other hints.  that makes fsck 
slow but effective, and in most cases, the journal analysis done when 
remounting after an unclean shutdown is enough to put it back on track.

i sure wish i could use XFS in more circumstances, but the needed 
hardware is prohibitive.

mfg zmi
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