----- Original Message -----
From: "Antonio Varni" <avarni@estalea.com>
To: centos@centos.org
Sent: Friday, November 16, 2007 9:06:52 AM (GMT+1000) Australia/Brisbane
Subject: [CentOS] IO causing major performance issues
Hello everyone.
I'm wondering what other people's experiences are WRT systems becoming
unresponsive (unable to ssh in, etc) for brief periods of time when
a large amount of IO is being performed. It's really starting to
cause a problem for us. We're on Dell PowerEdge 1955 blades - but this same
issue has caused us problems on PE1950, PE1850, PE1750 servers.
We're running Centos 4.5 right now. I know Centos 5 includes ionice, more
io scheduler/elevator selections like deadlock/etc. Perhaps that would
fix this issue. We're running the latest PERC firmware.
The specific issue I'm referring to at this point is on a system running
mysql. All mysql data files are on a netapp filer but mysql's tmp directory
is on local disk. Whenever a lot of temp tables are created (and thus
written and deleted from local disk quickly) we can't even log in to the
machine - and our monitoring system gets all freaked out and we get
lots of pages, etc... FYI this is two disks with hardware raid 1.
Is it just me? Or is this specific to Dell systems, or is this just
the state of the Linux kernel these days? Is there some magical patch
I can apply to make this issue go away :)
Thanks in advance for any insight into this issue.
Antonio
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Santa Barbara, CA 93101
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I have noticed similar behaviour on all sort of linuxes (in particular, ssh into the box is really slow when it's doing IO) and wondered why, but never really thought about investigating any further.
Unfortunately, I do a lot of work with solaris and the funny thing is that I have *never* seen a solaris kernel exhibit this sort of behaviour. Even if it is installed on normal IDE/SATA disks. And, in fact, even if installed on the exact same hardware.
Now I'm curious.....especially given that I'm right in the middle of pushing to get rid of solaris in favour of RHEL.