John,
We have been using 9840's for some months now for ADSM on OS390 host backing up
disk pools written to by many clients and have had a pretty good experience.
However I queried with STK the capacity tthat we were seeing the tapes filled
at. Here is a summnary of their reply. I would point out that the already
compressed data that it refers to is predominently netware data which is already
netware compressed on the netware clients giving on those boxes approx 4:1
compression.
So what it is saying is that if your clients already software compress then you
are not going to get the quoted figures, the 80gb. figure is for previously
uncompressed data.
Salesmen!!
John
John - it would appear that the 21 to 31GB reported capacity used from ADSM
reports is typical of software/precompressed data being written to 9840. There
are numerous references to a 30GB capacity reported by ADSM. But that is the
data written by ADSM, ADSM does not know what the data is, the drive compression
is improving things further but cannot give the same compression yield on
already compressed data as it can on straight data.
Your 31GB figure could represent up to 100GB of raw data input to ADSM. MVS
stats or 9840 have no way of knowing what the effective raw capacity is.
As a sanity check what was ADSM reporting for 36track etape??
I'm appending some collected thoughts (including yours) that I've culled from
STK world wide.
Tony Penn
Pre Sales Consultant StorageTek UK
work 01483 737429
mobile 0402 899553
fax 01483 737463
Tony_Penn AT StorageTek DOT com
"Doherty, John (ANFIS)" <jdohe1 AT ANFIS.CO DOT UK> on 14/02/2000 09:45:10
Please respond to "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>
To: ADSM-L AT VM.MARIST DOT EDU
cc: (bcc: John Naylor/HAV/SSE)
Subject: ADSM/9840 compression problem
Hi folks, we have recently installed StorageTek 9840 drives and each tape
has the capacity to hold 20GB native up to 80GB compressed. We thought this
an ideal medium for ADSM storage. I had set the device classes up to
accommodate 60GB (err on the catious side, 3:1 compression) with compression
set to yes.
We have tapes filling up at 19-21GB !!
Anyone experiencing this or could they give me any help on why this would be
the case?
Thank you in advance
> John Doherty. Tel: +44 (0) 141 275 7793
> Fax: +44 (0) 141 275 9199
> Email: JDohe1 AT Anfis.co DOT uk
>
> Technical Specialist, Storage Management L02S
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