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Another (Unrelated) IOWAIT Problem

Another (Unrelated) IOWAIT Problem

2006-02-22       - By Peter Ruprecht

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Reply:     1     2     3  




On Wed, 22 Feb 2006, John.B.Kelly wrote:

> Hello,
>
> We're using a Poweredge 700 running RHEL AS3 to NFS share some data. The
system does not have a 3Ware SATA controller so I don't think bugzilla bug
121434 (https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=121434) is
relevant. The problem (which is causing severe NFS client performace
degradation) is that when I run top, iowait is up at around 90 to 95%. There is
also audible hard-disk thrashing. If I discontinue NFS sharing from the
Poweredge, iowait goes down to almost 0. When I restart NFS sharing, iowait
stays low for an arbitrary amount of time and then goes up to 90/95% again.
There doesn't seem to be any correlation that I can establish between any
accessing of the NFS shared directories by NFS clients and when the iowait
parameter returns to 90/95%. Has anybody seen this before? I
> 'm currently running kernel 2.4.21-37.0.1.EL but also saw this problem with
some 2.4.21-27 kernels. I searched for solutions on the web and as a result I
've been playing with some kernel parameters in /proc/sys/vm/inactive_clean
_percent and /proc/sys/vm/pagecache (currently set to 100 and "2 10 20"
respectively) but this has not caused any improvement. The next 2 things which
I am considering trying is installing autofs on the NFS clients (to possibly
reduce network traffic) or else install a 2.6 kernel on the NFS server but
before I do either of these, I would really appreciate any advice from any RHEL
AS3 users who have seen this problem or even who could recommend an appropriate
next step in my troubleshooting.
>

Are any of your NFS clients RHEL 4 systems that have gam_server running?
That application can cause local disk thrashing if gam is monitoring local
files ... possibly it could also beat up the NFS server if it was trying
to monitor a mounted filesystem.

This is pretty much just a wild guess.  Note, as an aside, that general disk
performance is much better with 2.6 kernels, not just where the 3ware
controllers are concerned.

-Peter

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