AIX 5.3 IO Pacing

[rondebbs]

Hello, we have been having a problem with an AIX 5.3 server that is running SAS (statistical application). It shares an EMC cx380 array with several other servers/applications. The SAS system can do very heavy IO and tends to dominate the array and slowing performance for the other servers/applications.

With very little knowledge we turned on IO pacing using smit - Change/Show Characteristics of Operating System. We used a high water mark of 33 and a low water mark of 24 (this was the example used in the F1 help). This may be helping to throttle down the IO on SAS so the other servers can get better performance. If we wanted to throttle the SAS server even more would we simply increase the spread between the water marks - For example 40/10 rather than 33/24? Anything else we should be aware of?

 

[khalidaaa]

rondebbs,

The best range for the maxpout and minpout parameters depends on the CPU speed and the I/O system. I/O pacing works well if the value of the maxpout parameter is equal to or greater than the value of the j2_nPagesPerWriteBehindCluster parameter. For example, if the value of the maxpout parameter is equal to 64 and the minpout parameter is equal to 32, there are at most 64 pages in I/O state and 2 I/Os before blocking on the next write.

Have a look at this link for more info:

http://publib.boulder.ibm.com/infoc....aix.prftungd/doc/prftungd/disk_io_pacing.htm

Note that IO pacing is not the only way out of this! Have alook at more alternatives:

http://www.ibm.com/developerworks/aix/library/au-aixoptimization-disktun1/

Regards,
Khalid