On Thu, Jul 30, 2009 at 1:33 AM, Marcy Cortes<marcy.d.cor...@wellsfargo.com> wrote:
> Question, what is the value of using diag for swapping to vdisk? > Even if it is a more efficient driver, you're swapping to memory. How much > does it save? Hey, what's happening. Wasn't I supposed to ask those questions? ;-) I'm afraid the desire to do this comes from lack of performance data and combining different recommendations (assuming that 1+1=2 in Linux on z/VM Performance). Some of the observations relate to older Linux levels, and each time we publish that a "VM thing" performs better than the "LPAR thing" the folks in IBM went to change code to reverse that, one way or the other. When you swap to VDISK, the difference today between FBA and DIAG is marginal at real life swap rates (even swap into DCSS is in the same range). When performance does not make difference, ease of configuration does. With a fragile setup you run a bigger risk of breaking it and losing more than the savings you tried to make. > And how much swapping would you need to be doing for any savings to be > worthwhile? Wouldn't it be simpler to just increase the VM size to an amount > that minimizes swapping? Or are there servers you *want* swapping a lot for > some reason and if so why? Sure, buying more storage to avoid swapping is make some people happy. As an IBM Support person replied to a customer: "If you are swapping or paging, you don't have enough memory. Then anything can happen and I can't help you with that. Buy more..." ;-) It depends on the variation in memory requirements and the utilization of the server. If you travel with the entire family only once a year, it makes little sense to drive alone to the office every day in that big truck - (oh, maybe that analogy is not so obvious over there ;-) Rob -- Rob van der Heij Velocity Software http://www.velocitysoftware.com/ ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
