SDB
As always a default may or may not be what is best for the allocation
type. ISPF tends to need all the information in small blocks ie 10
records of 80 bytes (or somewhere there abouts) now the fair question
to ask why doesn't ISPH create records with more info in them and
that requires a history with ISPF and IBM and users.
If you would like a worse case is PARMLIB where history dictates and
IBM finally went with blocked.
There is no good answer to these issues but as others have indicated
that "virtual" DASD has all but transcended everything.
Except for special cases on highly active data sets the rules rules
have changed.
Ed
On Dec 7, 2013, at 11:49 AM, Paul Gilmartin wrote:
On Sat, 7 Dec 2013 01:56:56 +0000, DASDBILL2 wrote:
We can calculate the wasted space given the block size, average
number of blocks per track, average number of this, that, and the
other thing, but wasted space is meaningless and unknowable unless
you are using a SLED 3390 which means now at least 15, maybe 20-
year old disk drives. With the advent of RAID, the interrecord
gaps have been virtualized.
If gaps and other unused space are virtualized, there is no reason
for SDB
ever to choose a BLKSIZE other than 32760 (or nearest multiple of
LRECL).
I suspect there are various implementations of RAID: some may
virtualize
unused space; others keep images of entire tracks, however sparsely
used.
I tried the experiment I suggested: I created 10 mebers of 350
records.
With RECFM=FB,LRECL=80,BLKSIZE=27920 (chosen by SDB) the data
set used 10 tracks. When I forced to BLKSIZE=24000, it used 7 tracks.
Admittedly a deliberate worst case.
-- gil
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