On Tue, 31 Jan 2012 22:49:53 -0600, Barbara Nitz <[email protected]> wrote:
>>Writing to contiguous slots and over allocation is mentioned, but unless I >>missed it the "old" ROT (and health check) of not having more than 30% >>of the slots allocated is not specifically addressed. Certainly with 4K >>pages (for the most part) and 3390-27 (or bigger) that 30% ROT doesn't >>apply anymore? 50% of a mod-27 is still a helava lot of free slots. > >I think it still applies. My understanding has always been that the 30% usage >(after which paging effectiveness drastically drops) applies to the algorithm >used on the in-storage control blocks to pick the next free slot in a page >data set. Unless that algorithm was redesigned, 30% of 44.9GB per page dataset >is what you should not exceed (just as the health check says) in AUX usage. >Redesign of that is IMHO unlikely, just as using more than 2 IOs on a page >data set simultaneously would require (an unlikely) redesign. > That sounds right as far as the algorithm, but I thought the paging effectiveness was related to likelihood of not being able to find contiguous slots for group page outs after the 30% usage (based on "old" technology). So if I have 5 3390-27 locals and they are all equally used at 50%, the algorithms (CPU usage, not I/O) are going to pick one of them, then do the page outs. That paging will find contiguous slots and should be efficient. BTW, this is just an example, we still try to keep our 3390-27 local usage at 30% just like we always did with smaller local page datasets in the past. I wonder what if any studies on this have been done in the lab. It would be nice if an IBM performance expert like Kathy Walsh could weigh in. Regards, Mark -- Mark Zelden - Zelden Consulting Services - z/OS, OS/390 and MVS mailto:[email protected] Mark's MVS Utilities: http://www.mzelden.com/mvsutil.html Systems Programming expert at http://expertanswercenter.techtarget.com/ ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
