[CentOS] Filesystem writes unexpectedly slow (CentOS 6.4)

Tue Oct 14 02:50:46 UTC 2014
Joakim Ziegler <joakim at terminalmx.com>

On 13/10/14, 20:59, Keith Keller wrote:
> On 2014-10-14, Joakim Ziegler <joakim at terminalmx.com> wrote:
>>
>> So, if I use iozone -a to test write speeds on the raw device, I get results in
>> the 500-800MB/sec range, depending on write sizes, which is about what I'd expect.
>>
>> However, when I have an ext4 filesystem on this device, mounted with noatime and
>> data=writeback, (the filesystem is completely empty) and I test with dd, the
>> results are less encouraging:
>
> My first question would be, why not test the filesystem with iozone too?
> (And/or, test the device with dd.)  You may or may not come up with the
> same results, but at least someone can't come back and blame your
> testing methodology for the odd results.
>
> (Just as an aside, if your 6.4 box is on a public network, you should
> probably consider updating it as well, since many security and bug fixes
> have been issued since 6.4 was released.)
>
> If you are still getting poor results from ext4, you have at least two
> more options.
>
> ==Check with the ext4 mailing list; they're usually pretty helpful.
> ==Try your tests against xfs.  Try to make sure your tests are
> replicating your use cases as closely as you can manage; you wouldn't
> want to pick a filesystem based on a test that doesn't actually
> replicate how you're going to use the fs.

Googling shows some people who solved what seems like a similar problem with a 
kernel upgrade, so I'm going to try that. This box is on 2.6.32-358, and 
2.6.32-431.29.2 seems to be the newest. At least it's a factor to eliminate.

-- 
Joakim Ziegler  -  Supervisor de postproducción  -  Terminal
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