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Causes of high wait i/o

Posted on 2002-07-23
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Last Modified: 2013-12-06
I've got this voice application running on AIX.  ever so often you just have to restart that application since everything comes to almost a halt.  I did run just the basic sar.  The only thing i noticed was the wait i/o was 97%  and pct idle was 3%.  How do i determine what the causes are? This may be a seperate question, but how do i set up sar to give the best info plus i think it is supposed to give reports.
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Question by:xoxomos
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chris_calabrese earned 100 total points
ID: 7172782
Waiting for I/O is a red herring. It just means that the process is waiting for some bits to come off a disk, through a pipe, etc.

The Percent Idle, however, indicates that your system is under great CPU strain, which probably explains why your voice app can't keep up (i.e., can't get the CPU often enough).

If the voice app itself is the thing sucking up all the CPU, then your only solution is to run the app on a faster box.

Otherwise, the app could be setup so that it has real-time priority in the process scheduler. Unixen don't traditionally support this, but some systems like Solaris and HP-UX have been extended to support it. But I don't know if AIX supports it, and I don't know how you'd go about setting it up if it does.
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