On Feb 13, 2008, at 3:44 PM, GAVIN Darren * OPS EAS wrote:
Most of the Performance on tape drives can be accomplished by matching
the BUFNO= parameter to the Devices I/O Data Transfer Size. For your
model that's probably (most Tapes and VTS are) a 128kb size, so you
would want enough buffering to hold at least 1 128k Large Block.
So for a BLKSIZE=32768 file you would want a BUFNO=4 at minimum, but
would be better off with BUFNO=16 or BUFNO=32 (4 or 8 Large Blocks) as
Some VTS Units and the 256 track 3590E have a 256kb Transfer Size.
However DFSORT ignores any buffering (It has its own I/O context) on
both DASD and TAPE so no need to use it when doing sorts.
The other thing you can do is to add a step at start of job that will
Pre-Mount the tapes and then Retain them for any following steps,
using
IEFBR14 as a stub program, and the VOL=(,RETAIN) option mentioned
earlier.
There is also the /*setup card that can be used on some JES systems.
Darren
Darren,
I am fairly sure that the default for QSAM is 5 buffers if you
decrease it to 4 you will have a negative impact on performance.
Ed
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