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I don't remember about PT, but Performance Explorer (PEX) trace-type can
collect physical IO and logical IO data. With PT's PRTPEXRPT you can get a
good report on this. Otherwise, go to the raw data files. (That's way so
much fun - not exceptionally-well documented, tho' you should look at the
PT manual and a redbook from 1995 that is pretty good. Just remember to
start with QAYPETIDX, the trace index file, then join to others using the
common record number field, QRECN.). If you can afford the $6,000 per
annum, there's a thing called iDoctor that further processes the output of
PRTPEXRPT into very nice graphs and reports. You can download its user
guide for free, and that has a lot of good info.

If anyone is interested, I'm happy to discuss this stuff privately, to
mutual benefit, I hope. Or on this or another list, where appropriate. I'm
using this a lot in some products and can always learn more about this
mysterious area.

vhamberg@attbi.com
vhamberg@centerfieldtechnology.com

At 11:03 AM 7/1/02 -0400, you wrote:
>What with the disk controllers having cache memory, does anyone know if the
>WRKDSKSTS percentages reflect cache activity or actual disk arm activity ?
>
>The implication being that a cache that is 10% busy or 90% busy is
>inconsequential since it is all instant memory access, without any wait
>needed. ( especially when writing to the cache )
>
>The activity number that will give meaningful info is activity on the back
>end of the cache, where the disk arms put and get to the cache.  For
>example, how frequently is the cache full so that the next write to the
>cache must wait for cache data to be written to disk.  And how frequently do
>reads from the disk cache not find the data being sought in the cache,
>resulting in a wait for an actual disk read to be completed.
>
>Steve Richter



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