Bruce Black wrote:
At one time there was a definite problem with tape if the LRECL was
less than 18 bytes, as the data was treated as noise errors.
The limitation was on blocksize, not LRECL.
The restriction was on minimal physical blocksize, which is somewhat
different than constraining the defined blocksize for the file.
In particular, in the case of a RECFM FB dataset, the final physical
block can be a short block that contains only a single logical record,
so a minimum physical block constraint for FB files was the same as
putting that constraint on the minimal logical record size.
For a RECFM VB dataset, a short physical block containing a single
minimal record (in this case with length minimal lrecl + 4) can occur as
either the final block of the dataset or anywhere internally in the
dataset (all it takes is a minimal size record followed by a maximal
sized record that needs a block by itself). Again in this case a
minimum physical block constraint implies a similar minimal constraint
on a logical record size as well.
It is unlikely any of the old length constraints apply to files written
to cartridge drives with hardware compression, where the actual physical
blocks are "superblocks", chosen by the hardware and hidden from MVS.
...
--
Joel C. Ewing, Fort Smith, AR [EMAIL PROTECTED]
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO
Search the archives at http://bama.ua.edu/archives/ibm-main.html
