You got me. I keep forgetting that the 2 GB I/O boundry in z/VM 5.1 and below isn't the same as executing code.
Neither of these, have ever bitten me. The VM folks have been very good about keeping ahead of the curve, as far as I have been concerned. Tom Duerbusch THD Consulting >>> Dennis.L.O'[EMAIL PROTECTED] 3/17/2006 1:01 PM >>> Correction to item 1: z/VM 5.1 and below can support more than 2G of central storage in the LPAR, as long as you're on zSeries hardware. They just have to move pages below 2G when CP needs to do something with them, such as I/O. Dennis "Do you think it's a good idea, letting an Arab country take over our ports? This is like letting Bill Clinton be the manager of a Hooters." -- Jay Leno -----Original Message----- From: The IBM z/VM Operating System [mailto:[EMAIL PROTECTED] On Behalf Of Tom Duerbusch Sent: Friday, March 17, 2006 09:19 To: IBMVM@LISTSERV.UARK.EDU Subject: Re: VM Performance Question I don't know for sure if it really helps, but I have been saying the same thing for years. Setting expanded storage is a good thing for an actively paging system. Also by reducing the amount of central storage, would cause increased paging. But if you are not actively paging, why have expanded storage. But this is only good for: 1. If you are on z/VM 5.1 or under and have 2 GB or less in the LPAR. If you have more than 2 GB, then you have to configure expanded storage to use the rest, so it is a moot point. 2. You are not actively paging. IMHO, a few pages a second or a spike when something relatively rare happens (a new guest being IPL'ed), CICS being cycled, xedit a million line printout, etc. But when you start actively paging, then, for performance reasons, you do need to start configuring expanded storage. I have no proof, but I doubt that you will see any difference (a performance monitor will), unless you are paging a lot. I always question rules of thumb and other performance tidbits. What conditions do these solve, and am I even close to one of those conditions. There are many things that really only for large or heavy use, shops. Tom Duerbusch THD Consulting >>> [EMAIL PROTECTED] 3/15/2006 4:21 PM >>> The link below is a VM Performance article with the ending "Bottom Lines" recommendations. Has anyone done this and did it in fact improve performance? Bottom Lines |----------------------------------------------------------------------- -------| | | |For VM/ESA, if you have plenty of storage, little paging, a well tuned MDC, a | |consistent load, and a robust DASD paging configuration, then all real storage| |is most likely the best case. Otherwise, consider configuring some storage as | | expanded storage. A ballpark starting point is 25% of processor storage. You | | must configure anything above 2GB as expanded storage. | |----------------------------------------------------------------------- -------| |----------------------------------------------------------------------- -------| | | | For z/VM, you should still configure some storage as expanded. The 25% value | |may still be a good starting point. Most systems do not need more than 2GB of | | expanded storage regardless of the total storage available. Systems with no | | constraint below 2GB, can use less expanded storage. Constraint below 2GB | | often is indicated by significant paging to DASD and a large number of pages | | available above 2GB (as seen by QUERY FRAMES command or your favorite | | performance tool). In that case, you will want to add more expanded storage. | | You may also be able to free-up expanded storage by limiting the amount of | | expanded storage in use by minidisk cache (MDC) via the CP command SET MDC | | XSTORE or with a system configuration statement. | |----------------------------------------------------------------------- -------| www.vm.ibm.com/perf/tips/storconf.html TIA Jan Canavan
