Re: xfs_repair segfaults with ag_stride option

From: Tom Crane <T.Crane@rhul.ac.uk>
To: Eric Sandeen <sandeen@sandeen.net>
Cc: Christoph Hellwig <hch@infradead.org>,
	T.Crane@rhul.ac.uk, xfs@oss.sgi.com
Subject: Re: xfs_repair segfaults with ag_stride option
Date: Mon, 6 Feb 2012 11:19:07 +0000	[thread overview]
Message-ID: <4F2FB72B.9010209@rhul.ac.uk> (raw)
In-Reply-To: <4F2F6C00.5050108@sandeen.net>

Eric Sandeen wrote:
> On 2/5/12 6:50 PM, Tom Crane wrote:
>   
>> Hi Christoph,
>> Many thanks for the quick response and the patch. It was a big help.
>> I was able to repair our 60TB FS in about 30 hours. I have a couple
>> of questions;
>>
>> (1) The steps in the progress report seem a little strange. See the
>> attachment. Is this expected?
>>
>> (2) This may be a little out of band but I have heard second hand
>> reports from another sysadmin that the xfs tools which come with SLC5
>> (our current Linux distro) should not be relied upon and that SLC6
>> should be used. Our 60TB FS is significantly fragmented (~40%) and I
>> would very much like to run xfs_fsr on it. Given that I have built
>> the latest xfsprogs, is there any reason I should be afraid of
>> running xfs_fsr, on the FS which comes with SLC5? Unfortunately I
>> don't have ~60TB spare storage space elsewhere to backup the FS
>> before defragging. What would you advise?> 
>> Many thanks
>>     
>
> Newer tools are fine to use on older filesystems, there should be no
>   

Good!

> issue there.
>
> running fsr can cause an awful lot of IO, and a lot of file reorganization.
> (meaning, they will get moved to new locations on disk, etc).
>
> How bad is it, really?  How did you arrive at the 40% number?  Unless
>   

xfs_db -c frag -r <block device>

Some users on our compute farm with large jobs (lots of I/O) find they take 
longer than with some of our other scratch arrays hosted on other machines.  We also typically find many 
nfsd tasks in an uninterruptible wait state (sync_page), waiting for data to be copied in from the FS. 

> you see perf problems which you know you can attribute to fragmentation,
> I might not worry about it.
>
> You can also check the fragmentation of individual files with the
> xfs_bmap tool.
>
> -Eric
>   

Thanks for your advice.
Cheers
Tom.

>   
>> Tom.
>>
>> Christoph Hellwig wrote:
>>     
>>> Hi Tom,
>>>
>>> On Wed, Feb 01, 2012 at 01:36:12PM +0000, Tom Crane wrote:
>>>  
>>>       
>>>> Dear XFS Support,
>>>>    I am attempting to use xfs_repair to fix a damaged FS but always
>>>> get a segfault if and only if -o ag_stride is specified. I have
>>>> tried ag_stride=2,8,16 & 32.  The FS is approx 60T. I can't find
>>>> reports of this particular problem on the mailing list archive.
>>>> Further details are;
>>>>
>>>> xfs_repair version 3.1.7, recently downloaded via git repository.
>>>> uname -a
>>>> Linux store3 2.6.18-274.17.1.el5 #1 SMP Wed Jan 11 11:10:32 CET 2012
>>>> x86_64 x86_64 x86_64 GNU/Linux
>>>>     
>>>>         
>>> Thanks for the detailed bug report.
>>>
>>> Can you please try the attached patch?
>>>
>>>   
>>>       
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>>     
>
>   

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