 | | | Another (Unrelated) IOWAIT Problem | Another (Unrelated) IOWAIT Problem 2006-02-22 - By Arjan van de Ven
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On Wed, 2006-02-22 at 21:18 +0000, 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
this is not a "iowait problem".
it's an NFS/VM problem ;)
(it's like describing someone who has pneumonia which leads to a fever,
to having "fever disease")
in fact it's worse here; since IOwait isn't a problem, it's just cpu
idle time.
calling it by one of the measurements/symptoms rather than looking what
is really going on is only going to confuse many and actually is not
helping to get a solution. Like you already did to some extend, you
looked up "iowait" and at least you figured you had a different problem
because you didn't have a 3ware card)... many others don't make that
step ;(
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