W dniu 2011-10-10 05:30, Mingee, David pisze:
Hello All,
Anyone had success with performance gains in run time and fewer
tapes being created when using z/OS Large Block Interface(LBI)? We are on
R1.11 and have created tapes with blksize of 256k(262144) and the block count
is reduced by a factor of 8, but we do not see any improvements in elapsed time
or fewer tapes being created(20 output tapes at 32k and 20 output tapes at
256k). Am I missing something? IBM documentation states:
Taking advantage of LBI: You can improve the performance of tape data sets by
using the large block interface (LBI) for large block sizes. When the LBI is
available, the COBOL run time automatically uses this facility for those tape
files for which you use system-determined block size. LBI is also used for
those files for which you explicitly define a block size in JCL or a BLOCK
CONTAINS clause. Use of the LBI allows block sizes to exceed 32760 if the tape
device supports it.
It depends, as usually. I measured performance of BLKSIZE=256k vs 32k
and noticed small improvement. However your application may be to slow
to get benefits from LBI. Maybe your DASD is to slow - current tape
drives are damn fast for sequential output, special techniques are used
to slow them down when needed.
BTW: You mentioned COBOL. Do you really use tapes as input/output for
applications?
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Lodz, Poland
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