Okay, I get that. However, I seem to be using a high amount of Page Datasets and the only thing I can see is zFS. In fact I am right now trying to size the zFS environment so it uses a smaller foot print. There are no frequent SVC Dumps on this system.
I will ask for zFLASH to be looked at. Thanks Lizette > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On > Behalf Of Cheryl Walker > Sent: Monday, November 24, 2014 8:07 AM > To: [email protected] > Subject: Re: Page Data Set Sizes and Volume Types > > Hi Lizette, > > Did you take a look at that Techdoc? It shows you how to calculate the number of > slots. > > Regarding using larger rather than smaller data sets, it depends on what happens to > your online performance during an SVC dump. In most installations, the only paging > occurs during an SVC dump. If you can monitor performance during that time (e.g. > online response time) and amount of paging, you might be able to determine > whether a change in performance will affect you. > > Best regards, > Cheryl > > ====================== > Cheryl Watson > Watson & Walker, Inc. > www.watsonwalker.com > cell & text: 941-266-6609 > ====================== > > On Nov 24, 2014, at 9:35 AM, Lizette Koehler <[email protected]> wrote: > > Thanks to all with help on this topic. > > Cheryl. Thanks very much. I was hoping to find a formula to determine the number > of slots, but I think MXG can help with that. > > I also was trying to determine if I can swap out 20 Mod3s for 2 Mod27s and not > have to create little datasets on the Mod54. > > I have a sandbox and I will be attempting to arrange some validations of my > assumptions. > > Lizette > > > > -----Original Message----- > > From: IBM Mainframe Discussion List [mailto:[email protected]] > > On Behalf Of Cheryl Walker > > Sent: Monday, November 24, 2014 7:30 AM > > To: [email protected] > > Subject: Re: Page Data Set Sizes and Volume Types > > > > Hi Lizette, > > > > Here's an item from our latest Tuning Letter (2014 No. 3). This might > > help > a little. > > > > Page Data Set Usage > > > > Tom Kelman of Xerox Business Services, LLC asked: "I have heard that > > the process where the paging subsystem attempts to block pages > > together to > send them > > to the paging data sets went away around z/OS 1.7 or 1.8. Is that > > true, > and if so is it > > still necessary to keep the percent of local page space used down to 30%?" > > > > To answer the first part of his question, z/OS 2.1 still supports > > block > paging. The > > 30% number is to make the contiguous slot algorithm most efficient. > Contiguous > > slots are used even if block paging is not in play. > > > > To answer the second part of his question, yes, the recommendation is > still 30%, > > although it could be more or less. It's relatively easy to calculate > > the > best value for > > your installation. Here is an excellent paper on how to do the > calculation: Techdoc > > TD104728 (z/OS Availability: Managing SVC Dumps to Mitigate Exhausting > > the Paging Subsystem). > > > > It all has to do with SVC dumps. SRM will identify a storage shortage > > if > you use > > more than 70% of the page data sets. While taking an SVC dump, you > > don't > want to > > take more than 70% of the page slots. Therefore, IBM recommends that > > you > keep > > the total auxiliary dump space and paging space to less than 60% of > > the > slots. It > > really depends on how much storage you have, how big your SVC dumps > > are, > and > > how many concurrent dumps you are likely to experience. > > > > We asked Kathy Walsh, Distinguished Engineer at IBM's Washington > > Systems Center, whether the availability of Storage Class Memory (SCM) > > has any > effect on > > this recommendation. Her reply: > > > > If you have SCM on the LPAR then assuming its service time is faster > > it > will get > > most of the pages, except for VIO which is not written to SCM. So as > > far > as I am > > concerned the recommendation has not changed. For locals we still > > don't > want them > > more than 30% used. Of course with SCM it will be hard to get to 30% > unless there > > is a lot of VIO activity. With SCM there has been no change in the Aux > DASD IO > > support hence nothing has changed which would merit a change in > > recommendation. > > > > And while we're mentioning SCM, we want to remind you of our article > > in > Tuning > > Letter 2013 No 3 (IEASYSxx Update): > > > > [The IEASYSxx keyword] PAGESCM indicates whether and how much storage- > > class memory (SCM - also known as FlashExpress or zFlash) to allow for > paging > > data sets. We described zFlash, which is a priced (about $125K per 1.4 > > TB > in the > > U.S.) hardware feature on a zEC12, in our Tuning Letter 2013 No. 1, > > pages > 4-7. Our > > recommendation for zFlash was: > > > > RECOMMENDATION: If SVC dumps are hurting performance, if the start of > > day brings serious performance problems, or if you want to provide > > performance enhancements in Java, DB2, or IMS, you should consider > > Flash Express for > your > > zEC12. It has great potential, and I haven't heard of any downsides. > > > > Best regards, > > Cheryl > > > > ====================== > > Cheryl Watson > > Watson & Walker, Inc. > > www.watsonwalker.com > > cell & text: 941-266-6609 > > ====================== > > > > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
