What's the correllation between File I/O's and Disk I/O's

What's the correllation between File I/O's and Disk I/O's

Post by john_prend » Sat, 07 Aug 2004 19:36:55


Hi
We have a client that is getting poor response times.
But it's not consistant. One person may have no problems one day while
another is having huge delays, and the next day it's vice versa.
The system we have does a lot of data entry. Depending on the data
entered, a validation against files is required.
We've done a lot of investigation into this, and one thing that we
have noticed is that the number of Disk I/O's increases much faster
than the File I/O's requested.

One thing noticed was they had 9 disks, and disk 1 was going to 70-80%
utilisation (WRKDSKSTS), which in turn caused the other 8 disks to
increase in utilisation.

The iSeries is not reporting damaged objects, files or access paths.

Example
File I/O's Disk I/O's
Action 1: 155 127
Action 2: 230 478
Action 3: 285 400
Action 4: 340 377
Action 5: 420 1220
Action 6: 480 2720

Looking at the above example Actions 1-4 look OK to us (afte review
the program source for Read/Writes and updates). But Actions 5 & 6
have much more Disk I/O than we'd expect.
Should there be some sort of correllation between File I/O's and Disk
I/O's?
What governs Disk I/O is it the OS?
Is there some configuration changes we might be able to make to help
alleviate the problem?

TIA
John
 
 
 

What's the correllation between File I/O's and Disk I/O's

Post by qgenesis » Sat, 07 Aug 2004 23:55:04

two things immediate. straspbal will balance the files by usage across
disks more evenly some files are mostly found on arm1 and disks were
added later as well as applications. i could offer an elegant proof of
this but i hate to type. you can tell it to balance for a period of
time if you are pressed (dedicated system stuff, here) additionally
you can block file read and write given right circumstances check rick
turners optimizing batch performance on AS/400 in ibm area (search
performance). if you are writing dups to unique and then 1 up the
sequence number to success (for example) is many i/o fix that stuff.
tunnel carpal setting in, i hope this is not to cryptic. :-) ron

 
 
 

What's the correllation between File I/O's and Disk I/O's

Post by GB » Sun, 08 Aug 2004 19:21:11


Its not a dedicated process... (and isn't it called STRDSKRGZ?)



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What's the correllation between File I/O's and Disk I/O's

Post by Robert Com » Tue, 10 Aug 2004 23:05:30

> Its not a dedicated process... (and isn't it called STRDSKRGZ?)

STRDSKRGZ and STRASPBAL aren't the same thing -- STRASPBAL distributes the
data across disks, you only need it when you put a new disk in. STRDSKRGZ
is like DEFRAG on a PC. (kind of opposite of each other except neither are
at the disk level.)

- Bob Comer