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Date: Thu, 07 Aug 2008 18:08:59 -0400
From: Mark Mielke <mark@mark.mielke.cc>
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To: Andrej Ricnik-Bay <andrej.groups@gmail.com>
CC: Scott Marlowe <scott.marlowe@gmail.com>,
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Subject: Re: file system and raid performance
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Andrej Ricnik-Bay wrote:
> 2008/8/8 Scott Marlowe <scott.marlowe@gmail.com>:
>   
>> noatime turns off the atime write behaviour.  Or did you already know
>> that and I missed some weird post where noatime somehow managed to
>> slow down performance?
>>     
>
> Scott, I'm quite aware of what noatime does ... you didn't miss a post, but
> if you look at Mark's graphs on
> http://wiki.postgresql.org/wiki/HP_ProLiant_DL380_G5_Tuning_Guide
> they pretty much all indicate that (unless I completely misinterpret the
> meaning and purpose of the labels), independent of the file-system,
> using noatime slows read/writes down (on average)

That doesn't make sense - if noatime slows things down, then the 
analysis is probably wrong.

Now, modern Linux distributions default to "relatime" - which will only 
update access time if the access time is currently less than the update 
time or something like this. The effect is that modern Linux 
distributions do not benefit from "noatime" as much as they have in the 
past. In this case, "noatime" vs default would probably be measuring % 
noise.

Cheers,
mark

-- 
Mark Mielke <mark@mielke.cc>


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Andrej Ricnik-Bay wrote:
<blockquote
 cite="mid:b35603930808071457x40334261uad77dab2623f2757@mail.gmail.com"
 type="cite">
  <pre wrap="">2008/8/8 Scott Marlowe <a class="moz-txt-link-rfc2396E" href="mailto:scott.marlowe@gmail.com">&lt;scott.marlowe@gmail.com&gt;</a>:
  </pre>
  <blockquote type="cite">
    <pre wrap="">noatime turns off the atime write behaviour.  Or did you already know
that and I missed some weird post where noatime somehow managed to
slow down performance?
    </pre>
  </blockquote>
  <pre wrap=""><!---->
Scott, I'm quite aware of what noatime does ... you didn't miss a post, but
if you look at Mark's graphs on
<a class="moz-txt-link-freetext" href="http://wiki.postgresql.org/wiki/HP_ProLiant_DL380_G5_Tuning_Guide">http://wiki.postgresql.org/wiki/HP_ProLiant_DL380_G5_Tuning_Guide</a>
they pretty much all indicate that (unless I completely misinterpret the
meaning and purpose of the labels), independent of the file-system,
using noatime slows read/writes down (on average)</pre>
</blockquote>
<br>
That doesn't make sense - if noatime slows things down, then the
analysis is probably wrong.<br>
<br>
Now, modern Linux distributions default to "relatime" - which will only
update access time if the access time is currently less than the update
time or something like this. The effect is that modern Linux
distributions do not benefit from "noatime" as much as they have in the
past. In this case, "noatime" vs default would probably be measuring %
noise.<br>
<br>
Cheers,<br>
mark<br>
<br>
<pre class="moz-signature" cols="72">-- 
Mark Mielke <a class="moz-txt-link-rfc2396E" href="mailto:mark@mielke.cc">&lt;mark@mielke.cc&gt;</a>
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