Chase, John wrote:
-----Original Message-----
From: IBM Mainframe Discussion List On Behalf Of Mike Bell
[ snip ]
The single biggest issue I remember was blksize on loadlibs.
After much discussion, we moved them manually with copymod to
set new blksizes.
IBM has been recommending BLKSIZE=32760 for load libraries for at least
a decade.
<snip>
Absolutely true for system software load libraries. I don't
recall that we ever recommended a specific block size for other
load libraries, except perhaps by thoughtlessly omitting the "for
system software target libraries" phrase in an informal setting
(say, here in IBM-MAIN).
For example, using 32760 for other load libraries can cause some
head-scratching and extra work during device conversions...which,
oddly enough, is the current topic! That's one reason we never
recommended it in the general case.
Another is that system software target libraries tend to be built
on the device types from which they will be used, and tended by
sysprogs who might remember to reblock them during a conversion
effort. Application libraries, by contrast, might bounce around
among different device geometries under DFSMShsm control or be
moved by storage administrators who are moving *so* much stuff at
once that fine-tuning isn't a reasonable option. For these
libraries, a reasonable submultiple of the track lengths of the
different devices--that is, one that yields reasonable space
utilization on each one--might well be better choice of block
size. (Ever wonder where all those 6K-ish block sizes came from?
Now you know.)
In any case, for block sizes that are not reasonable submultiples
of the two track lengths in question, you should always move load
libraries between different device types using IEBCOPY COPYMOD,
*not* COPY. Otherwise, particularly for data sets with large
block sizes, the difference in track lengths will result in truly
abysmal space utilization for those data sets having load modules
with lots of long text blocks and less-than-optimum space
utilization for most of the rest.
Also, to avoid RC4s from COPYMOD that would make a duly diligent
sysprog from looking at (and up) messages that don't matter,
always use PARM=SPCLCMOD with COPYMOD.
John Eells
z/OS Technical Marketing
IBM Poughkeepsie
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