Message-ID: <4FB6D17A.7070408@sandeen.net>
Date: Fri, 18 May 2012 17:47:22 -0500
From: Eric Sandeen <sandeen@sandeen.net>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:12.0) Gecko/20120428 Thunderbird/12.0.1
MIME-Version: 1.0
To: =?ISO-8859-1?Q?Niccol=F2_Belli?= <darkbasic@linuxsystems.it>
CC: xfs@oss.sgi.com
Subject: Re: How to recover data from an xfs partition
References: <4FAE9DBF.1090505@linuxsystems.it> <20120518143143.GN16099@sgi.com> <4FB66430.9040202@linuxsystems.it> <4FB68AF6.1090303@sandeen.net> <4FB6B7AB.8030405@linuxsystems.it>
In-Reply-To: <4FB6B7AB.8030405@linuxsystems.it>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit

On 5/18/12 3:57 PM, Niccolò Belli wrote:
> Il 18/05/2012 19:46, Eric Sandeen ha scritto:
>> the file backing it - what was that stored on?
> 
> It was a raw image created with dd and stored on an SSD (ext4). Some
> of the virtual machines were on traditional hard disks instead
> (ext4).
> 
> Only the running virtual machines got damaged, the main filesystems
> are perfect.
> 
>> What it was that did the scribbling
> 
> Rebooting. A simple, stupid reboot after upgrading Xen. While
> rebooting the system I got some kind of kernel panic and I had to use
> magic sysrq keys (remount read-only, sync, reboot).

Well - somehow the first sector of the xfs image got junk written into it...
hard to say how that happened, but the magic number lives in the
first sector of the xfs image hosted on ext4, and it was junk post-reboot.

I have never seen xfs corrupt _itself_ this way.  TBH I'd be as likely to
blame the SSD, as anything.  But you also have to have all of the data
integrity bits set up properly all along the virt stack to survive
a panic or power loss w/o corruption after the fact.

-Eric