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Re: xfs_repair of critical volume

To: Eli Morris <ermorris@xxxxxxxx>
Subject: Re: xfs_repair of critical volume
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Mon, 01 Nov 2010 19:14:22 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <00C51060-5205-4E95-B27C-8E31468ED45C@xxxxxxxx>
References: <75C248E3-2C99-426E-AE7D-9EC543726796@xxxxxxxx> <4CCF3D68.6060201@xxxxxxxxxxx> <00C51060-5205-4E95-B27C-8E31468ED45C@xxxxxxxx>
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On 11/1/10 6:32 PM, Eli Morris wrote:
> 
> On Nov 1, 2010, at 3:21 PM, Eric Sandeen wrote:
> 
>> On 10/31/10 2:54 AM, Eli Morris wrote:
>>> I have a large XFS filesystem (60 TB) that is composed of 5
>>> hardware RAID 6 volumes. One of those volumes had several drives
>>> fail in a very short time and we lost that volume. However, four
>>> of the volumes seem OK. We are in a worse state because our
>>> backup unit failed a week later when four drives simultaneously
>>> went offline. So we are in a bad very state. I am able to mount
>>> the filesystem that consists of the four remaining volumes. I was
>>> thinking about running xfs_repair on the filesystem in hopes it
>>> would recover all the files that were not on the bad volume,
>>> which are obviously gone. Since our backup is gone, I'm very
>>> concerned about doing anything to lose the data that will still
>>> have. I ran xfs_repair with the -n flag and I have a lengthly
>>> file of things that program would do to our filesystem. I don't
>>> have the expertise to decipher the output and figure out if 
>>> xfs_repair would fix the filesystem in a way that would retain
>>> our remaining data or if it would, let's say t!
>> 
>> 
>> One thing you could do is make an xfs_metadump image,
>> xfs_mdrestore it to a sparse file, and then do a real xfs_repair
>> run on that. You can then mount the repaired image and see what's
>> there. So from a metadata perspective, you can do a real-live
>> repair run on an image, and see what happens.
>> 
>> -Eric
> 
> Hi Eric,
> 
> Thanks for the suggestion. I tried is out and this is what happened
> when I ran xfs_mdrestore:
> 
> # xfs_mdrestore -g xfs_dump_image vol5_dump xfs_mdrestore: cannot set
> filesystem image size: File too large #
> 
> Any ideas? Is the file as large as the volume or something? I think
> you had a really good suggestion. If you know how to make this work,
> I think that would be great.

Guessing you tried to create it on an ext3 filesystem?

The file has a maximum offset == the size of the filesystem, but it is
sparse so does not take up that much disk space.

ext3 can't go beyond a 2T file offset.

Making the file "dump_image" on an xfs filesystem should do the trick.

-Eric

> thanks,
> 
> Eli
> 
> 

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