SUMMARY: 2.4 "iowait" state

From: Gregory Bond (
Date: Tue Dec 05 1995 - 01:56:16 CST

Original question (abridged):
>Both "top" and "xmeter" show CPU utilization as 100%, but vmstat shows about
>80% idle. The difference seems to be that top (and I assume xmeter) class
>"iowait" cpu usage as busy, whereas vmstat considers it idle.


Iowait means the CPU is idle, but there are processes waiting on short-term IO
(usually disks) which will run just as soon as the IO is finished. If another
CPU-bound job came along it would run, but the disk system is flat out.
Basically, the system is io-bound and has CPU cycles to spare.

This is not really an error, and is probably unavoidable in database
applications. Actually, I kind of like "iowait" as a concept, and can
understand how the different programs treat it differently.

A couple of people also mentioned "sar" as a better tool than vmstat for
Solaris 2.

Thanks to those that responded.


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