> >To be precise: ASM reserves 2 exposures *per pagedataset* not per > >volume (i.e. 2n-1 Aliasses per volume), since/so you can allocate more > >than 1 pagedataset on one volume. We do so to fill 3390-9s and -27s with > >pagedatasets. > > I beg to disagree. :-) HiperPAV works on a per-IO-basis in the > hardware, so ASM cannot 'reserve' an exposure (anymore). HiperPAV is > for faster I/O turnaround and for reduction of IOS queuing times by > giving another SSCH another 'exposure'. No SSCH, no HiperPAV usage. > If no I/O is started because ASM knows there is one outstanding (as > was the case in the past) then HiperPAV is effectively not used. > Other than for the second case that Jim Mulder had detailed in the > past. Hence my question if that is still true or if ASM now starts > as many IOs as needed to get paging requests filled.
For a page data set on a HiperPAV device, ASM creates two sets of channel program control blocks. If a single page read request come along while the first set is in use, ASM will use the second set to start another channel program to do the single page read. The purpose is to avoid having a single page read need to wait for a long string of pageouts to complete before it can be started. Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: INFO IBM-MAIN
