joerg.brehe

How long can I use the Record descriptor word (RDW) or block
descriptor word (BDW) for the deblocking of records?

I read, there are some ideas by IBM, to change the geometry of DASD.
However, as the need for more and faster storage, there is some
pressure to eliminate the rstrictions imposed by the CHK architekture.

use it?


thanks forward
jörg

david bond

Jörg,

If you are using BSAM, then you should probably update your programs
to support the Large Blocksize Interface, which has been available
for tape since DFSMS 1.3. You need to set up a DCBE with the
DCBEULBI bit set to request the LBI before opening the DCB and then
test the DCB DCBESLBI bit after OPEN to see if the LBI is available
for the device. The DEVTYPE service can also be used to determine
if the LBI is available.

The BDW allows a block size of up to 2147483647. The new BDW
format has the high-order bit set to 1 and the block size in the remaining
31 bits. There are also new ways of getting and setting the block size
for RECFM=U.

As long as your programs can support the LBI using BSAM or QSAM
and your programs don't examine or calculate TTR values, you should
not have any problems with geometry changes.

David Bond - Tachyon Software LLC - http://www.tachyonsoft.com

colin campbell

I expect that you can use the structure of Variable Blocked files as
long as you want to. This structure has been available since
essentially the beginning of S/360 architecture. I think that spanned
records may have been added during that time, but I am not positive.

IBM places a high importance on compatibility. I know of programs that
still run which were written, compiled, and linked over 30 years ago.
While IBM does not support ISAM, there are still companies using it.
BDAM files are still being processed. BSAM and QSAM are still
supported, and I've not read of any [lans to stop supporting them.

All of this is not to say that new file organizations and DASD
architectures will not be developed in the future. But if you continue
to have access to the information you are using in variable blocked
format, I am pretty certain you'll be able to process it.