ADSM and STK Iceberg dasd
1995-12-07 09:42:40
From - Raymond Raw at The Mutual Group
Technical Services, 519/888-3900 x3505
InterNet Address - CATMGRWR AT IBMMAIL DOT COM
CC: IBMMAIL /INTERNET
SUBJECT: ADSM and STK Iceberg dasd
We currently have 4 ICEBERG systems totaling 840 gigs. We're very
happy with them. We were part of the early beta program and have
been running ICEBERG's for 2 years. They perform pretty much as STK
says although we've seen some inconsistencies with PAGE datasets on
them.
We've had ADSM databases on ICEBERG right from the start without any
problems. However, there is one major point of consideration when
putting ADSM databases on ICEBERG. (I suspect that RAMAC might have
the same problem.)
The ICEBERG size (200gig, 300gig etc.) is based on an assumption of 3
to 1 data compression within the box. The real round and brown
backing a 200gig ICEBERG is only about 75gig in size. (The 3 to 1
ratio has actually changed with the newer boxes.) At any rate, the 3
to 1 compression ration is generally very conservative and for most
data we achieve better compression ratio. However, if you put
precompressed ADSM data onto an ICEBERG, you don't achieve the 3 to 1
ICEBERG compression and the box fills up faster than expected. The
result being that a 200gig ICEBERG might only store 150gigs of
compressed ADSM data.
In the last few months STK has moved to newer faster compression
chips that do a better job of ADSM precompressed data so this problem
might be insignificant now. My suggestion would be to talk to STK
specifically about ADSM data. They are certainly aware of what we
experienced. Your STK rep can also run one of their field utilities
against your 3390 databases and tell you exactly what compression
rations you should achieve on the ICEBERG.
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