retired mainframer wrote:
<snip>
With a blocksize of 3120, 15 blocks fit on a track for a total of 585
records. Almost a 50% improvement. My preference is 6160 (reasonably
efficient for both 3390 and 3380 - yes we have very old archived datasets
which occasionally must be restored) which will allow 616 records per track.
We previously had a similar discussion for load modules where 32760 is
optimal for the Binder but not necessarily for IEBCOPY.
(Interestingly, perhaps, this topic keeps coming up, both inside and
outside IBM, over two decades after I did the original research that led
to our recommendation to block system software load libraries at 32760.
That recommendation stands.)
It's only IEBCOPY COPY operations that can behave suboptimally when
copying load modules across different device types when moving blocks
that are not good submultiples of the destination device's track length.
This should be largely irrelevant today unless people still have 3380s
defined (does anyone, still?), but see below.
IEBCOPY COPYMOD, though, has no trouble at all reblocking load modules
that are "blocked at"* 32760, and behaves in much the same way the
Binder does. Whenever you copy a load library it costs nothing to use
COPYMOD instead of copy. And, if you do that after allocating the
destination load library at a higher block size than the source load
library, you just might gain performance and reduce the space required
for the data set. (This stops being true once the size of the largest
possible text block falls below the destination data set's block size.)
* Both the Binder and IEBCOPY use the block size only to set the maximum
size of a text block to be written, and write shorter ones under some
conditons. All the other records are typically written in short blocks.
--
John Eells
z/OS Technical Marketing
IBM Poughkeepsie
ee...@us.ibm.com
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