W dniu 2013-07-23 12:32, Jantje. pisze:
Taking the risk of starting another flame war here...
Are there still any shops that have actual SLED? In today's world of emulated
DASD, would it really still hold true that using smaller block sizes is
actually wasting space? After all, these bytes are in the end physically
written to FBA devices with 512 byte sectors, no? In the old days, there were
inter-record gaps that took up space, but is this still the case? And even if
the emulation is so good that it simulates those, what is happening with the
actual capacity of the physical disks. Is that being eaten by simulated IRG?
3390 (E)CKD disks are emulated nowadays, but the emulation covers also
nter-records gaps. So it's still waste of REAL space if you user
RECFM=F,LRECL=80. You will waste great part of emulated tracks doing so.
Note, there was (still is?) architecture developed by Storagetek, sold
as Iceberg, IBM RVA, STK, SVA, SVAA, etc.In this architecture all data
are compressed before written to disk, so, your tracks will still be
half-emptuy, but they will take less real stroage than full-populated
ones. Unfortunately those arrays had some "issues" with both scalability
and performance, especially for sequential processing. BTW: funny things
became occuring when your data were not as compressible as DASD
engineers assumed.
BTW2: nowadays the largest FBA (real) disks use 4k sectors.
Compatibility problems with older OSes apply as usual. ;-)
--
Radoslaw Skorupka
Lodz, Poland
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