I/O Pacing Setting for HA Causes Performance Problems


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 time-outs in an HA environment, it may prove to cause performance problems for AIX.

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:

Enter smitty
Select System Environments
Select Change / Show Characteristics of Operating System
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 time-outs.