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Re: xfs_repair of critical volume

To: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Subject: Re: xfs_repair of critical volume
From: Eli Morris <ermorris@xxxxxxxx>
Date: Fri, 12 Nov 2010 15:01:47 -0800
Cc: xfs@xxxxxxxxxxx
In-reply-to: <201011121422.28993@xxxxxx>
References: <75C248E3-2C99-426E-AE7D-9EC543726796@xxxxxxxx> <4CCD3CE6.8060407@xxxxxxxxxxxxxxxxx> <864DA9C9-B4A4-4B6B-A901-A457E2B9F5A5@xxxxxxxx> <201011121422.28993@xxxxxx>
On Nov 12, 2010, at 5:22 AM, Michael Monnerie wrote:

> On Freitag, 12. November 2010 Eli Morris wrote:
>> The filesystem must be pointing to files that don't exist, or
>> something like that. Is there a way to fix that, to say, remove
>> files that don't exist anymore, sort of command? I thought that
>> xfs_repair would do that, but apparently not in this case.
> 
> The filesystem is not optimized for "I replace part of the disk contents 
> with zeroes" and find that errors. You will have to look in each file if 
> it's contents are still valid, or maybe bogus.
> 
> I find the robustness of XFS amazing: You overwrote 1/5th of the disk 
> with zeroes, and it still works :-)
> 
> Now that you are in this state, I'd recommend you
> a) make a *real* *tape* *backup*
> You learned it the hard way: a disk copy is no backup, at least I hope 
> you learned that lesson
> b) Maybe also copy all your files to another system, or you trust your 
> backup from a) very much
> c) reinitialize the full array. Really recreate every array, 2 b sure 
> all your RAIDs work this time.
> d) copy your data backup - either from the other copy of b), or from the 
> tape backup in a)
> 
> Then you will see a correct view of disk space used and which files are 
> still there. Now you must check every files content, some will have 
> bogus content.
> 
> -- 
> mit freundlichen Grüssen,
> Michael Monnerie, Ing. BSc
> 
> it-management Internet Services: Protéger
> http://proteger.at [gesprochen: Prot-e-schee]
> Tel: +43 660 / 415 6531
> 
> // ****** Radiointerview zum Thema Spam ******
> // http://www.it-podcast.at/archiv.html#podcast-100716
> // 
> // Haus zu verkaufen: http://zmi.at/langegg/


Hi Michael,

thanks for the advise. 

Let me see if I can give you and everyone else a little more information and 
clarify this problem somewhat. And if there is nothing practical that can be 
done, then OK. What I am looking for is the best PRACTICAL outcome here given 
our resources and if anyone has an idea that might be helpful, that would be 
awesome. I put practical in caps, because that is the rub in all this. We could 
send X to a data recovery service, but there is no money for that. We could do 
Y, but if it takes a couple of months to accomplish, it might be better to do 
Z, even though Z is riskier or deletes some amount of data, because it is cheap 
and only takes one day to do.


This is a small University lab setup. We do not have access to a lot of 
resources. We do have a partial tape backup of this data, but...

a) The time it takes to back up the full 62 TB is long enough to tape that it 
is not really much of a help. Most days we have hundreds of GBs generated and 
removed. We back up about 12 TB of the most important files, and ones that 
don't rapidly change, but our tape backup system just can not keep up with 
everything. Yes, it would be *fantastic* to have a full tape backup system that 
is practical and has the capacity to deal with everything. Because we have had 
so many problems with our storage lately, the backup is somewhat stale, 
partial, and a little suspect. Still, it is there and I will investigate what 
can be recovered from it.

b) I don't have another system to copy the files to. Our disk backup is screwed 
up and that is all of our storage. We do have a tape backup, as I mentioned, 
and while it is theoretically possible to dump to tape, rebuild the RAID 
arrays, then dump back, the practical aspects of this process make this a so-so 
option. Realistically, it would take more than a month to accomplish. It is a 
possibility, but is not a really great option.

c) We are working on making sure everything is working OK. I think the power 
output from our UPS might be problematic. We are definitely investigating that, 
because it could be behind all these crazy problems.

d) Checking every files' content manually is not something that is going to 
work. It would, literally, take years.

Again, thanks for any advise. I'm not trying to be negative, just realistic in 
what I have to work with in terms of resources and time. 

Would de-fraging the filesystem remove those zeroed files from the filesystem? 
Does anyone make a XFS utility program that might help? Maybe an XFS utility 
that can be used to remove zeroed files from the filesystem? Or remove files 
that are stored in that one bad LVM volume?

thanks very much,

Eli


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