I/O Pacing Setting for HA Causes Performance Problems

Problem

For purposes of HACMP I/O pacing, the high and low water marks are tuned to other values besides zero. As this may be helpful for timeouts in an HA environment, it may prove to cause performance problems for AIX.

Solution

No fixed values exist for setting I/O pacing. As with any tuning parameters, pacing values may need to be set differently for different computing environments. The I/O pacing and syncd changes will affect performance within all facets of the AIX system.

You can, however, change the water marks by following the steps below:

1. Enter smitty
2. Select System Environments
3. Select Change / Show Characteristics of Operating System
4. Set both the high and low water marks to 0 (zero).

Setting the water marks to zero turns the I/O pacing off, thereby improving local performance. Keep in mind, however, that HA may need to be set to other values because the zero settings may lead to more DMS timeouts.

[ Doc Ref: 9822543612088     Publish Date: Feb. 16, 2001     4FAX Ref: none ]