You might want to take a look at vm.swappiness setting. (see discussion here a few months ago). We found one of ours munched through it (not as fast as plowed) at a setting of 60 but not at a setting of 20 where it seemed to stay put.
Marcy "This message may contain confidential and/or privileged information. If you are not the addressee or authorized to receive this for the addressee, you must not use, copy, disclose, or take any action based on this message or any information herein. If you have received this message in error, please advise the sender immediately by reply e-mail and delete this message. Thank you for your cooperation." ________________________________ From: The IBM z/VM Operating System [mailto:ib...@listserv.uark.edu] On Behalf Of Martin, Terry R. (LOCKHEED MARTIN Performance Engineering/CTR) (CTR) Sent: Thursday, April 30, 2009 5:35 PM To: IBMVM@LISTSERV.UARK.EDU Subject: Re: [IBMVM] SWAPGEN Scott Wrote: A real disk might make real sense with an ill-behaved, unpredictable guest that is causing you swapping headaches. This is exactly why I want to allocate a real disk. I understand the theory behind what Rich and Barton are saying but in practice all workloads are not created equally. In my case I am planning for what I already know can happen (saw it during testing) so knowing this that is the only reason I am considering a real disk as a last precaution. Of course I am working with the application developers to enhance the efficiency of the application which is the REAL BANG FOR THE BUCK! Thanks to all for all of the responses it is much appreciated. Thank You, Terry Martin Lockheed Martin - Information Technology z/OS & z/VM Systems - Performance and Tuning Cell - 443 632-4191 Work - 410 786-0386 terry.mar...@cms.hhs.gov <mailto:terry.mar...@cms.hhs.gov> ________________________________ From: The IBM z/VM Operating System [mailto:ib...@listserv.uark.edu] On Behalf Of Scott Rohling Sent: Wednesday, April 29, 2009 9:51 PM To: IBMVM@LISTSERV.UARK.EDU Subject: Re: SWAPGEN 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 <rsmrc...@wi.rr.com> 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 <bar...@vm1.velocity-software.com> 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// //terry.ma...@cms.hhs.gov <mailto:terry.ma...@cms.hhs.gov>// -- Rich Smrcina
