Dave, you are probably correct in being cautious about making a sweeping change without looking for evidence first. For more details on the PAV support that went out with the APAR you referenced, see http://www.vm.ibm.com/perf/reports/zvm/html/520pav.html. Remember that if there is no queueing on I/O in VM, there is no benefit from this PAV support. So if the I/O is queued in VSE, this won't benefit. The minidisk cache aspect is interesting. I imagine at one time you had dedicated perhaps for V=R and I/O Assist. Since that doesn't apply anymore, there might be value in looking at MDC. I'd start first with just getting a feel for the read/write ratios, since only reads have a chance to benefit from MDC. Since this is VSE, it would be limited to full track cache of MDC. The record level MDC does not apply here. We also learned recently that PAV and MDC do not mix as well as we would like. Watch this space.
Bill Bitner - VM Performance Evaluation - IBM Endicott - 607-429-3286
