Mike,
We use PAV for volumes containing CMS minidisks. We turned it on a few months
ago on a system that we acquired with our last merger, and the user was quite
pleased. It took a couple of hours off of their nightly batch. PAV is also on
for volumes that contain SFS minidisks. It doesn't help for volumes that have
SFS data minidisks (storage group 2+), because those are full packs, but it
doesn't seem to hurt anything. Our catalog and log disks are a couple hundred
cylinders each, and there are other CMS minidisks on those volumes. I presume
we're getting some benefit there.
Dennis
"Christmas dawned clear and cold; lovely weather for killing Germans, although
the thought seemed somewhat at variance with the spirit of the day." -- War as
I knew it, by Gen. George S. Patton, Jr.
-----Original Message-----
From: The IBM z/VM Operating System [mailto:[email protected]] On Behalf
Of Mike Walter
Sent: Monday, December 20, 2010 08:33
To: [email protected]
Subject: [IBMVM] General CMS minidisks and SFS on PAV DASD?
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
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