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Re: Issues and new to the group

To: Ronnie Tartar <rtartar@xxxxxxxxxxxx>
Subject: Re: Issues and new to the group
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Thu, 26 Sep 2013 09:23:17 -0500
Cc: stan@xxxxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <101601cebabc$8acb99a0$a062cce0$@host2max.com>
References: <0e4201cebaae$24873680$6d95a380$@host2max.com> <5244234D.1010603@xxxxxxxxxxxxxxxxx> <100f01cebaba$0ae84280$20b8c780$@host2max.com> <101601cebabc$8acb99a0$a062cce0$@host2max.com>
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On 9/26/13 8:30 AM, Ronnie Tartar wrote:
> Stan, looks like I have directory fragmentation problem.
> 
> xfs_db> frag -d
> actual 65057, ideal 4680, fragmentation factor 92.81%
> 
> What is the best way to fix this?

http://xfs.org/index.php/XFS_FAQ#Q:_The_xfs_db_.22frag.22_command_says_I.27m_over_50.25._Is_that_bad.3F

We should just get rid of that command, TBH.

So your dirs are in an average of 65057/4680 or about 14 fragments each.
Really not that bad, in the scope of things.

I'd imagine that this could be more of your problem:

> The
> folders are image folders that have anywhere between 5 to 10 million images
> in each folder.

at 10 million entries in a dir, you're going to start slowing down on inserts
due to btree management.  But that probably doesn't account for multiple 
seconds for
a single file.

So really,it's not clear *what* is slow.

> It takes about 2.5 to 3.5 seconds to write a single file.

strace with timing would be a very basic way to get a sense of what is slow;
is it the file open/create?  How big is the file, are you doing buffered or
direct IO?

On a more modern OS you could do some of the tracing suggested in
http://xfs.org/index.php/XFS_FAQ#Q:_What_information_should_I_include_when_reporting_a_problem.3F

but some sort of profiling (oprofile, perhaps) might tell you where time is 
being spent in the kernel.

When you say suddenly started, was it after a kernel upgrade or other change?

-Eric

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