We've always avoided using PAV volumes for general user (non-fullpack) CMS minidisks. Instead we've only used DASD defined as 3390-3 so that I/O queueing is minimized. That choice was in part due to management decisions.
Over the past weekend we needed to move some z/VM DASD quickly -- and the target DASD was already defined as PAV DASD. The z/VM CP Planning and Administration manual clearly states that "z/VM Paging and SPOOLing operations do not take advantage of PAV." (no argument here). We'll still plan to keep page and SPOOL volumes on non-PAV 3390-3 DASD. But the same manual also states that "When multiple CMS volumes are defined on a real PAV volume, I/O operations by CMS can be concurrently scheduled on any real PAV base or alias subchannel by z/VM. The CMS user does not need to take any action for this to occur." Well, that's "book larn'in". Can anyone provide real-life results of using PAV volumes for general-purpose CMS user minidisks, and... for SFS filespaces? Do you see real I/O improvement for those apps? If so, the next time we're asked we might recommend larger 3390 volumes, mod 9's or 27's (depending on the number of available paths) to permit larger minidisks without SFS overhead, and improved SFS performance. Thanks! Mike Walter Aon Corporation The opinions expressed herein are mine alone, not my employer's. The information contained in this e-mail and any accompanying documents may contain information that is confidential or otherwise protected from disclosure. If you are not the intended recipient of this message, or if this message has been addressed to you in error, please immediately alert the sender by reply e-mail and then delete this message, including any attachments. Any dissemination, distribution or other use of the contents of this message by anyone other than the intended recipient is strictly prohibited. All messages sent to and from this e-mail address may be monitored as permitted by applicable law and regulations to ensure compliance with our internal policies and to protect our business. E-mails are not secure and cannot be guaranteed to be error free as they can be intercepted, amended, lost or destroyed, or contain viruses. You are deemed to have accepted these risks if you communicate with us by e-mail.
