In
<746510224.45656.1370914746772.javamail.r...@sz0127a.westchester.pa.mail.comcast.net>,
on 06/11/2013
at 01:39 AM, DASDBILL2 <[email protected]> said:
>On output, the blocks are all written with the same blocksize except
>possibly the last. This causes the reading in of such a file with
>constant block size expectations to be possible.
>On input, a short block that is not the last block causes an I/O
>error because of the previous sentence.
That's true only for FBS, not for VBS.
>This sounds like an illogical/impossible scenario. There should
>always be enough bytes left on the track to write a completely fully
>block, as spanned=standard= a fixed block size
Not even close. The fact that both use the letter S and the same bit
does not mean that they are in any way similar, much less identical.
VMS mau in practice lead to a lot of blxks of the maximum size, but
that is not part of the definition or of the code.
>If after writing the last full block on a track there is at least
>one more byte of the last segment that needs to be written, it will
>be written on the next track even if there is still room on the
>current track for this very short block. If it were written on the
>same track, then that would mean that were one too many blocks on
>that track, and reading that track back in would cause the last
>short block to be missed, as enough read commands or read operations
>would only be built in the channel program to read the predicted
>number of blocks on that track before switching to the next track.
That's not even a good guess; it has nothing to do with the way BSAM
and QSAM build channel programs.
--
Shmuel (Seymour J.) Metz, SysProg and JOAT
Atid/2 <http://patriot.net/~shmuel>
We don't care. We don't have to care, we're Congress.
(S877: The Shut up and Eat Your spam act of 2003)
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