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Re: xfs_fsr, sunit, and swidth

To: Dave Hall <kdhall@xxxxxxxxxxxxxx>
Subject: Re: xfs_fsr, sunit, and swidth
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Fri, 12 Apr 2013 19:51:23 -0500
Cc: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
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On 4/12/2013 12:25 PM, Dave Hall wrote:
> Stan,
> 
> IDid this post get lost in the shuffle?  Looking at it I think it could
> have been a bit unclear.  What I need to do anyways is have a second,
> off-site copy of my backup data.  So I'm going to be building a second
> array.  In copying, in order to preserve the hard link structure of the
> source array I'd have to run a sequence of cp -al / rsync calls that
> would mimic what rsnapshot did to get me to where I am right now.  (Note
> that I could also potentially use rsync --link-dest.)
> 
> So the question is how would the target xfs file system fare as far as
> my inode fragmentation situation is concerned?  I'm hoping that since
> the target would be a fresh file system, and since during the 'copy'
> phase I'd only be adding inodes, that the inode allocation would be more
> compact and orderly than what I have on the source array since.  What do
> you think?

The question isn't what it will look like initially, as your inodes
shouldn't be sparsely allocated as with your current aged filesystem.

The question is how quickly the problem will arise on the new filesystem
as you free inodes.  I don't have the answer to that question.  There's
no way to predict this that I know of.

-- 
Stan

> Thanks.
> 
> -Dave
> 
> Dave Hall
> Binghamton University
> kdhall@xxxxxxxxxxxxxx
> 607-760-2328 (Cell)
> 607-777-4641 (Office)
> 
> 
> On 04/03/2013 10:25 AM, Dave Hall wrote:
>> So, assuming entropy has reached critical mass and that there is no
>> easy fix for this physical file system, what would happen if I
>> replicated this data to a new disk array?  When I say 'replicate', I'm
>> not talking about xfs_dump.  I'm talking about running a series of cp
>> -al/rsync operations (or maybe rsync with --link-dest) that will
>> precisely reproduce the linked data on my current array.  All of the
>> inodes would be re-allocated.  There wouldn't be any (or at least not
>> many) deletes.
>>
>> I am hoping that if I do this the inode fragmentation will be
>> significantly reduced on the target as compared to the source.  Of
>> course over time it may re-fragment, but with two arrays I can always
>> wipe one and reload it.
>>
>> -Dave
>>
>> Dave Hall
>> Binghamton University
>> kdhall@xxxxxxxxxxxxxx
>> 607-760-2328 (Cell)
>> 607-777-4641 (Office)
>>
>>
>> On 03/30/2013 09:22 PM, Dave Chinner wrote:
>>> On Fri, Mar 29, 2013 at 03:59:46PM -0400, Dave Hall wrote:
>>>> Dave, Stan,
>>>>
>>>> Here is the link for perf top -U:  http://pastebin.com/JYLXYWki.
>>>> The ag report is at http://pastebin.com/VzziSa4L.  Interestingly,
>>>> the backups ran fast a couple times this week.  Once under 9 hours.
>>>> Today it looks like it's running long again.
>>>      12.38%  [xfs]     [k] xfs_btree_get_rec
>>>      11.65%  [xfs]     [k] _xfs_buf_find
>>>      11.29%  [xfs]     [k] xfs_btree_increment
>>>       7.88%  [xfs]     [k] xfs_inobt_get_rec
>>>       5.40%  [kernel]  [k] intel_idle
>>>       4.13%  [xfs]     [k] xfs_btree_get_block
>>>       4.09%  [xfs]     [k] xfs_dialloc
>>>       3.21%  [xfs]     [k] xfs_btree_readahead
>>>       2.00%  [xfs]     [k] xfs_btree_rec_offset
>>>       1.50%  [xfs]     [k] xfs_btree_rec_addr
>>>
>>> Inode allocation searches, looking for an inode near to the parent
>>> directory.
>>>
>>> Whatthis indicates is that you have lots of sparsely allocated inode
>>> chunks on disk. i.e. each 64 indoe chunk has some free inodes in it,
>>> and some used inodes. This is Likely due to random removal of inodes
>>> as you delete old backups and link counts drop to zero. Because we
>>> only index inodes on "allocated chunks", finding a chunk that has a
>>> free inode can be like finding a needle in a haystack. There are
>>> heuristics used to stop searches from consuming too much CPU, but it
>>> still can be quite slow when you repeatedly hit those paths....
>>>
>>> I don't have an answer that will magically speed things up for
>>> you right now...
>>>
>>> Cheers,
>>>
>>> Dave.
> 
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