Re: xfs_fsr, sunit, and swidth

[Dave Hall <kdhall@binghamton.edu>]

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?

Thanks.

-Dave

Dave Hall
Binghamton University
kdhall@binghamton.edu
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@binghamton.edu
> 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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