Re: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).

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 Public Discussion Forum


Re: DASD Upgrades

IDMS does not currently support a file size greater than 64k tracks. We
have MOD-9 volumes which yield 150,000 tracks, but as Dan mentioned, we
keep them to under half a volume. However, the 64K track limit comes
out less than that.

We are limiting our large areas to 126,000 pages per file (instead of
the first guess of 128,000). Note that 126,000 divides evenly by 2, 3,
4, 5, 6, 7, 8, 9, 10, 12, 14 and 15, so it won't yield any fractional
tracks for any of these page sizes. =20

In practicality, we try to stick to 1/6, 1/5, 1/4, 1/3 or 1/2 track page
size. The 126,000 magic number allows us to initially allocate, for
example, a 13k page size for 1/4 track, but still be able to XPAGE it up
to 27k and stay below the 64k track limit.

As an aside, if you go to combine your files, you may already know that
you can just copy them, concatenating the input files and writing output
to fewer files as desired. We use SYNCSORT, which allows us some
control over the output files.

Jim Ritterbusch
Database Administrator
44 Old Ridgebury Rd.
Lee Farms Building
Danbury, CT 06810
T +01 203 546 4370
F +01 203 546 4499