On Oct 31, 2007, at 10:24 AM, GAVIN Darren * OPS EAS wrote:
I beg to differ right back, the default buffering is 2, according
to the
IBM Manuals. Your shop might have changed that through SMS. Some
places
do that.
<Snip>In truth, the physical geometry is largely
Unknown and most of the data is actually returned from some level of
cache,
where blocksizes mean nothing (since gaps don't exist).</Snip>
And I will differ with you on this point as well, as I've done my own
testing of Buffering sizes based on Data Transfer Sizes (that are
readily available in the manuals) and that matching them is the most
efficient way to do I/O. Once the Data leaves the cache of the
devices,
it is transferred at a certain size/rate. Matching that size with
additional buffers means that less actual I/O requests are made to the
channel.
Darren
IBM made the default for QSAM data sets (20 or so years ago) to 5 and
the default is for chained scheduling (for QSAM ) at the same time.
This was accomplished by integrating SAMe into DFSMS.
Ed
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