It depends! I think you have to study your perf data and decide where your i/o contention is. We don't have it like we used to (pre IBM DS8000 and FICON ) --- have moved on to just CPU and memory issues :)
We've moved most of our disks to mod 9 (all of prod Linux and about 1/2 the traditional CMS users) and the last 3 TB that went in I had them do mod 27 (makes creating large linux filesystems easier). Not using PAV anywhere. We just don't see the i/o queue that would warrant the effort. On the dev/test system with 100 linux virtual servers and not enough memory (24G real), we have about 50 mod 3's for paging. I don't suspect moving that to 16 mod 9's would be that much different. 16 is still pretty spread out. Now, if I had 3 page vols, I woudn't dream of putting them on 1 mod 9 :) It is a bit confusing for the perf guys though ---- since disk size does not show up in the perf data!!! And, I understood SFS to work like Kris said. We have both 3s and 9s in our SFS - we always give it the whole vol (minus cyl 0 of course ). Marcy Cortes "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." -----Original Message----- From: The IBM z/VM Operating System [mailto:[EMAIL PROTECTED] On Behalf Of O'Brien, Dennis L Sent: Wednesday, June 20, 2007 6:32 PM To: IBMVM@LISTSERV.UARK.EDU Subject: [IBMVM] PAV and SFS Our DASD people have asked if they can replace our 3390-3 size DASD volumes with 3390-9's. My tentative answer is that most of the volumes that contain minidisks can be moved, if the new DASD has PAV. CP areas such as paging should remain on 3390-3. Our SFS servers have 3338-cylinder minidisks, one per volume. My initial thought is that I could put 3 of them on a 3390-9 with two PAV aliases, and the SFS server could do one I/O to each minidisk at the same time, just like it can when the minidisks are on separate volumes. In the recent "dasd 3390 -27" thread, Kris Buelens said, "For SFS though (and probably DB2) PAV is maybe of limited help: a given SFS server will start only one I/O to all its minidisks on the same disk." Is that really true? Does an SFS server look at the real devices or volsers that its minidisks are on, and only start an I/O to one minidisk on a volume at a time? Dennis O'Brien The three R's of Windows problem resolution: Retry, Reboot, Reinstall.