DASD Upgrades

Discussion created by ca.portal.admin on Feb 4, 2009
Our service provider announced plans to upgrade DASD hardware from mod-3
(3,339 cyl) to mod-L (32,760 cyl). =20

Currently we have many multi-file areas with some exceeding 50 files.
The general approach is to keep allocation down to roughly 12,500 tracks
(quarter volume) for each file. I was told this allowed for flexibility
when having to perform these migrations (and there's probably other
reasons) but I'm not convinced this is a good way to manage our database

Would it be practical to allocate DB files to the volume's maximum size
when necessary? Any general rules to follow when allocating large

Brian Hirman
R16.0 SP4 z/OS 1.9

IDMS 3rd-party providers forum


Re: DASD Upgrades
"Brian, in addition to all of the good ideas already posted on this
question, consider the issue of performance.

If a large database is heavily used and allocated on relatively few
spindles, you have set yourself up for device contention and/or cache
overrun problems, in which case disk performance goes into the dumper
really fast due to I/O queuing and long seek times on large files.

I would concur with Dan's suggestion to keep individual file sizes
manageable ( <= 25K tracks ?) and place files across volumes and
channels as much as possible to balance I/O loading. You can then
mix-and-match less heavily-used files with your ""heavy-hitters"" to get
reasonable overall space usage while maintaining acceptable performance.

If you are not already familiar with tools and techniques for monitoring
and managing I/O load balancing, consult your ""friendly neighborhood
sysprog"" or contact me off the list.

Hal Govan
Senior Database Administrator
Reed Elsevier - Technology Services
Phone: (937) 865-7820