On Wed, 5 Jul 2006 12:08:58 -0500, Tom Marchant <[EMAIL PROTECTED]> wrote:
>
> >FBA rules.
>
> That depends upon how it would work. Would each block start
> immediately after the last, or at the beginning of the next
> physical block? What about crossing extents? How would a
> PDS work, or anything else that uses TTR (or MBBCCHHR)?
>
I think the model for this is PDSE, which ignores the programmer's
logical blocking and simply stores records. I believe it's possible
to create and write a PDSE with one block size in the DCB, then read
it with a different block size. The driver reblocks on-the-fly
as it fills the programmer's buffer. I hope, with no evidence,
that PDSE records span physical blocks and thus tracks, cylinders,
and extents.
It's existing and proven technology, though doubtless it has broken
some legacy code that's sensitive to device geometry. Reliability
and integrity problems with PDSE often discussed here likely arise
from other sources than the flexible blocking.
Using {Q|B}SAM to read or write a UNIX file works similarly. Alas,
the BPAM support for UNIX files is read-only.
-- gil
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