Thanks Bill. I will say that I am in fact seeing some of the same issues that you mention as possible issues when running above the memory limit in my current configuration at 130G.
Most of this is due to our major over commit ratio hence paging delays for us. So my hope was to reduce the over commit by adding more real memory, but I am starting to get concerned now doing this. I don't what else to do to relieve this other than adding more memory. What is your thought, should I be worried ? Thank You, Terry Martin Lockheed Martin - Citic z/OS and z/VM Performance Tuning and Operating Systems Support Office - 443 348-2102 Cell - 443 632-4191 -----Original Message----- From: The IBM z/VM Operating System [mailto:[email protected]] On Behalf Of Bill Holder Sent: Monday, October 11, 2010 6:21 PM To: [email protected] Subject: Re: Max REAL STORAGE for z/VM LPAR Known scalability issues as size increases above 256GB primarily involve z/VM's page replacement algorithms including the "Reorder" and "Demand Scan" functions; known symptoms include things like excessive system CPU overhead decreasing overall throughput, and temporary guest hangs as CP tasks process resources belonging to guests with very large numbers of pages resident. Other symptoms may be possible as well, depending on workload characteristics; we haven't experimented with, measured, and analyzed all that many different kinds of workloads in such large environments. Regarding running right at 256GB, that is a supported environment, so should any issues occur, contact us via the usual support channels and we'll work with you to resolve them. Some of the same scalability issues can indeed manifest to some extent at sizes below 256GB, depending on workload, but generally to a degree that is more manageable and can be "tuned around". We understand the need to increase the supported storage size above the current 256GB limit. - Bill Holder, z/VM Development, IBM Endicott On Mon, 11 Oct 2010 17:00:36 -0400, Martin, Terry R. (CMS/CTR) (CTR) <[email protected]> wrote: >So the question is if for some reason you go over that 256G say to 265G what issues will you see, and how will the manifest themselves? > >And if I stay right at 256G will I see any issues being that it is right at the max? > > > >Thank You, > >Terry Martin >Lockheed Martin - Citic >z/OS and z/VM Performance Tuning and Operating Systems Support >Office - 443 348-2102 >Cell - 443 632-4191 > >
