Friday, June 03, 2005

disk IO

Have you tried "iostat/sar" to see on which disk huge number of I/O
operation are executed. "iostat -P" can even give report for each disk
partition. Then you may decide which application program causes that based
on your knowledge of applications on your server.

Use "serv" (service time, in fact it's response time) in their report as an
indicator of disk I/O performance, if it keeps great than 30 (ms), you may
think about to distribute I/O operations on different disk, use disk mirror
and etc.

If a thread (or process) is waiting for one
or more outstanding i/o's to complete, it is
not using ("occupying" to use your term) any
CPU. It is suspended.

Iowait means precisely that the CPU is available.


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