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On 09/19/2011 06:39 PM, Jim Kinney wrote:
<blockquote
cite="mid:CAEo=5PwU7HtBU2bD95YBY5zrSv8hPpv71QVSmcnYf5NYNFadXg@mail.gmail.com"
type="cite">
<p>Is it one journal write per file or per inode used per file?</p>
<div class="gmail_quote">On Sep 19, 2011 4:24 PM, "David
Tomaschik" <<a moz-do-not-send="true"
href="mailto:david@systemoverlord.com">david@systemoverlord.com</a>>
wrote:<br type="attribution">
> On Mon, Sep 19, 2011 at 3:19 PM, John Heim <<a
moz-do-not-send="true" href="mailto:john@johnheim.net">john@johnheim.net</a>>
wrote:<br>
>> What (if anything) does it mean if iotop shows
that the process<br>
>> doing the most disk I/O is kjournald? Actually, on 4
partitions that I have<br>
>> on an ISCSI array, the kjournald process is the top I/O
on each.<br>
>><br>
>> I'm thinking of setting the noatime option in my fstab.<br>
> <br>
> It means that the journal on those disks is being written
to a lot.<br>
> Typically, you'll see this with lots of small writes. Each
write<br>
> requires the following:<br>
> <br>
> 1) Write change to journal.<br>
> 2) Write change to filesystem.<br>
> 3) Mark change as done in journal.<br>
> <br>
> So that's 2 journal writes for every FS write.<br>
</div>
</blockquote>
I'm not sure, to be honest. But I suspect it doesn't matter, as the
multiple journal entries are likely to fit in a single block and
form one logical journal write anyway.<br>
<br>
John -- if you don't need atime, then noatime does offer a
performance benefit. Alternatively, relatime is a nice
middle-ground:<br>
<br>
Update inode access times relative to modify or change
time. Access time is only updated if the previous<br>
access time was earlier than the current modify or
change time. (Similar to noatime, but doesn't break mutt<br>
or other applications that need to know if a file has
been read since the last time it was modified.)<br>
<br>
Since Linux 2.6.30, the kernel defaults to the
behavior provided by this option (unless noatime was speci‐<br>
fied), and the strictatime option is required to
obtain traditional semantics. In addition, since Linux<br>
2.6.30, the file's last access time is always
updated if it is more than 1 day old.<br>
<br>
(Assuming, of course, your kernel is older than 2.6.30. Otherwise,
as stated above, you already have relatime.)<br>
<br>
<pre class="moz-signature" cols="72">--
David Tomaschik, RHCE, LPIC-1
System Administrator/Open Source Advocate
OpenPGP: 0x5DEA789B
<a class="moz-txt-link-freetext" href="http://systemoverlord.com">http://systemoverlord.com</a>
<a class="moz-txt-link-abbreviated" href="mailto:david@systemoverlord.com">david@systemoverlord.com</a></pre>
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