Lizette Koehler wrote:
I have a project to review all the virtual tapes in the VTS and see which
tape datasets could go on dasd.
I am using CA1 to get the LRECL, BLKSIZE and BLKCNT to determine how many
bytes are on the tape. Then dividing that by the number of bytes per track
to get a rough estimate.
Is there a better way of doing this? I have over 100,000 tapes to review
and I am trying to make sure I have a good process.
Or is there a different formula I should be using other than
bytes = lrecl * blksize * blkcnt (and if blkcnt = 0 I
set blkcnt = 1)
As others have observed, the LRECL doesn't matter.
If you will use the same block size for each data sets as was used to
write it to tape, there is a formula to use to determine how many tracks
will be used on disk. But, it is much easier to use one of the
reference cards' sets of tables that show blocks per track at different
block sizes for keyed and unkeyed records to predict disk space for
fixed block data. If you can't lay hands on a 3390 reference card, or
find one of the 3390 or later storage books with the same tables, DTS
has tables in their "Storage Administration z/OS Pocket Reference," and
perhaps you can find a copy of that.
For variable blocked data, including RECFM=U, I am afraid that by far
the easiest way to see how much DASD space will be used is to simply
load the data sets and look afterward. The distribution of block sizes
around the mean, and the order in which differently sized blocks occur
in the data, will affect space utilization considerably. This could be
done programattically by reading the tape and calculating the space used
as the blocks are read but this is a complex undertaking and probably
not worth the effort.
If you use the largest possible block sizes for variably blocked data,
you will likely overpredict the amount of DASD space many of them
require--which might be better than underpredicting it, I suppose.
--
John Eells
z/OS Technical Marketing
IBM Poughkeepsie
ee...@us.ibm.com
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