Originally posted by: tech100

What are the recommendations for I/O pacing settings on AIX 5.3 run on modern P7 hardware? Still keep them AIX 5.3's defaults 0/0 or tune it?
Could I have any benefit of changing it to higher values on the AIX 5.3 run on P7 box?

maxpout 0 HIGH water mark for pending write I/Os per file True
minpout 0 LOW water mark for pending write I/Os per file True
Default for AIX 6.1 are :
maxpout 8193
minpout 4096
Anyone using such values in AIX 5.3?

regards.T.

Originally posted by: niella

Hi,

I/O pacing is helpful when there are multiple workloads, users or processes that compete for time and resources. The extreme cases would be workloads where response times are critical (needs lower values), or large individual I/O bound batches (needs higher values, or disable pacing altogether).

One thing is sure - the old guideline of 33/24 can drastically inhibit I/O throughput, and I would not use it on P6/P7 systems that makes use of a SAN.

I have done quite a lot of research on this and would recommend using the AIX 6 defaults (even on AIX 5.3), or 256/513 as a start on an environment that necessitates lower values, such as a HACMP cluster.

Here are some really helpful IBM documents:
AIX 6.1 performance management guide (p232, table containing throughput figures)
https://www-304.ibm.com/support/docview.wss?uid=isg3T1000163
https://www-304.ibm.com/support/docview.wss?uid=isg1IY94866

Regards,
Niel

Originally posted by: tech100

thx.

I was wondering why in HACMP 5.4.1 there was still 33/24 recommendation:

"Although the most efficient high- and low-water marks vary from system to system, an initial
high-water mark of 33 and a low-water mark of 24 provides a good starting point. These
settings only slightly reduce write times and consistently generate correct fallover behavior
from the HACMP software."