Right - I got that from Barton's post. Consider that there are times when using a real disk might make sense .. I'm just not big on blanket statements... Dedicating a resource is not always a big waste and does not always benefit one to the detriment of the rest. It's a balancing act and it takes all the tricks in the bag to keep it from falling over. A real disk might make real sense with an ill-behaved, unpredictable guest that is causing you swapping headaches. That's what I was trying to point out..
Maybe I'd stay quiet if I saw some qualifiers like 'in general' when people talk about BIG/REAL WASTE. Guidelines are nice, but I object to them being presented as 'rules'. I'll shuddup now ;-) Scott On Wed, Apr 29, 2009 at 6:16 PM, Rich Smrcina <[email protected]> wrote: > The biggest benefit of z/VM is to virtualize resources as much as > possible. Dedicating a resource to a specific guest is a big waste and > benefits one to the detriment of all the rest. It would be much better to > allocate all virtual disk swap for the Linux guests, then allocate the disk > that would have been dedicated to swap as page space. That way everyone > wins. > > > Scott Rohling wrote: > > Maybe -- but having a real disk (and setting an alert for that) helps > isolate the issue to a single guest rather than affecting critical shared > resources (in this case memory/paging) when a guest starts swapping more > than normal or than it 'should'. > > I like the idea of having a 'failover' swap area on real disk -- whether > you have a single VDISK or 2 prioritized ahead of it. I guess whether it's > waste of resource depends on your POV.. But your point is taken.. > > Scott > > On Wed, Apr 29, 2009 at 4:42 PM, Barton Robinson < > [email protected]> wrote: > >> giving real disks to swap is a real waste of resource. It is much better >> to take the "extra disk resource" that you allocate but never want to use, >> and assign it to z/VM paging to enhance your paging subsystem. Then define >> two vdisks for swap, prioritize them, and set an alert when the 2nd disk is >> being used. >> >> Martin, Terry R. (LOCKHEED MARTIN Performance Engineering/CTR) (CTR) >> wrote: >> >>> Hi >>> >>> >>> I am using SWAPGEN to define by z/Linux VDISKS I also want to define a >>> real disk for swap. My question is can I use SWAPGEN to define a swap on >>> real DASD? If you have an example of the control card syntax to accomplish >>> this that would be great? >>> >>> //Thank You,// >>> >>> >>> //Terry Martin// >>> >>> //Lockheed Martin - Information Technology// >>> >>> //z/OS & z/VM Systems - Performance and Tuning// >>> >>> //Cell - 443 632-4191// >>> >>> //Work - 410 786-0386// >>> >>> //[email protected] <mailto:[email protected]>// >>> >>> >>> >> > > > -- > Rich Smrcina >
