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Old 08-27-2008, 11:12 PM   #1
procfs
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Trace IO waits


Hi

I am have a 4 cpu 12G HP ProLiant DL580 G3, running Redhat AS3 (U 7).

When I do a top I can see some percentage if IO waits, can some one tell me or point to a document the will tell me how to do a trace on the process or processes which causing this IO wait

by the way the CPU utilization is over 90%

Thanks

Best regards
 
Old 08-28-2008, 01:01 AM   #2
syg00
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Just because you see "iowait" doesn't mean anybody is actually waiting on I/O. Semantics and statistics - what a mix ...
iowait says the CPU is idle, and there is I/O yet to complete. Possibly independent (and non related) events.

If you want to see what tasks are in uninterruptable sleep (usually disk I/O) try this
Code:
top -b -n 1 | awk '{if (NR <=7) print; else if ($8 == "D") {print; count++} } END {print "Total status D: "count}'
To find out what task(s) is/are doing the most I/O, you'll need a recent kernel with taskstats enabled - try iotop.py or collectl.
 
Old 08-28-2008, 03:58 AM   #3
procfs
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hi syg00

Thanks for the reply, but I am new to all this is there a document that I can refer to, at least get me started
 
  


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