Disk IO issues

[Stephen John Smoogen]

On Thu, Jan 1, 2009 at 12:17 AM, Mike McGrath <mmcgrath at redhat.com> wrote:
> On Thu, 1 Jan 2009, James Antill wrote:
>
>> On Wed, 2008-12-31 at 14:42 -0600, Mike McGrath wrote:
>> > Lets pool some knowledge together because at this point, I'm missing
>> > something.
>> >
>> > I've been doing all measurements with sar as bonnie, etc, causes builds to
>> > timeout.
>> >
>> > Problem: We're seeing slower then normal disk IO.  At least I think we
>> > are.  This is a PERC5/E and MD1000 array.
>> >
>> > When I try to do a normal copy "cp -adv /mnt/koji/packages /tmp/" I get
>> > around 4-6MBytes/s
>>
>>  This _might_ not be "IO" in a normal sense, -a to cp means:
>>
>>  file data + file inode + ACLs + selinux + xattrs [+ file capabilities]
>>
>> ...esp. given that you aren't getting large IOWait times, you might want
>> to strace -T the cp and do some perl/whatever on the result to see what
>> is eating up the time.
>
> Even with non cp type things (like a bacula backup) it just doesn't seem
> as fast as I would expect it to be.  I've never actually done trending at
> this level / scale on a filesystem / drive before.  So I really don't have
> a good baseline except that it just seems slow to me.

Well bacula should be doing the same thing as a cp in that it needs to
log all those things (ACL, selinux, xattrs, mother maiden name, etc).
Normally I have found that the bigger the disk the slower the copies
on journaled file systems. I don't currently have anything as big as
you have (this is over a TB correct?) but the speed fixes used to be
changing block sizes and journal parameters to allow for speed through
(oh and turning off certain hardware parameters in the raid controller
to allow for writethroughs there.


> Other then the much faster direct block access and the large file reads, I
> don't have much else to go on that makes me think its slow.
>
>>  This is a straight 5.2, yeh?
>>
>
> Correct.
>
>        -Mike
>
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-- 
Stephen J Smoogen. -- BSD/GNU/Linux
How far that little candle throws his beams! So shines a good deed
in a naughty world. = Shakespeare. "The Merchant of Venice"