W dniu 2013-07-22 18:08, Ed Jaffe pisze:
A customer (mildly) complained thatsome of our product allocations
still use BLKSIZE=3120. I vaguely remember trying to change all of
them to BLKSIZE=0 many years ago (probably before OS/390) and running
into some issues with certain IBM utilities. Unfortunately, I can't
remember the specifics.
In starting to revisit this again, I noticed numerousoccurrences of
'3120' in IBM help and documentation. For example, the TSO/E RECEIVE
command HELP claims that the log data set must be BLKSIZE=3120:
<TSO/E RECEIVE command HELP>
LOGDATASET You may specify an alternate data set to be
used for the logging of the transmitted data.
This data set will be created if it does not
exist. The data set should be created with
a logical record length of 255, a record format
of VB and a blocksize of 3120.
...
LOGDSNAME You may specify an alternate data set to be
used for the logging of the transmitted data.
This data set will be created if it does not
exist. The data set should be created with
a logical record length of 255, a record format
of VB and a blocksize of 3120.
</TSO/E RECEIVE command HELP>
Is this just outdated help? Or does this restriction still exist?
is z/OS still a "mine field" filled with subtle dependencies on
BLKSIZE=3120?
Well, IMHO it's not restriction, it is just allocation default. Good
default in very old days, but not very bad today.
Note, The difference between ~3k and optimal ~27k seem to be large, but
the effects (performance, space used) give no big difference.
BTW: DB2, LOGGER, MQ, and many many VSAM exploiters do use blocks 4kB.
Is it far from 3kB?
Of course you can try the above datasets with other (SDB) blocksize, and
I bet nothing will break. Why didn't they change it? Well, it time to
re-start the following subthreads:
- TSO is moribound
- if it isn't broken don't fix it (see latest implementation as IMBED
for catalogs).
Regards
--
Radoslaw Skorupka
Lodz, Poland
--
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