ADSM-L

Re: IBM vs. Storage Tek

2002-08-16 11:22:43
Subject: Re: IBM vs. Storage Tek
From: "Prather, Wanda" <Wanda.Prather AT JHUAPL DOT EDU>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Fri, 16 Aug 2002 10:39:51 -0400
Reminder:

Even if you are using collocation, it is NOT true that you need a tape for
every client.
The number of tapes used is controlled by the MAXSCRATCH parameter on the
storage pool.

In our case, we have more clients than we have slots available in the
library!
And the larger your tapes are, the less practical it is to dedicate a whole
cartridge to a client.

For example, if you have 400 clients and set maxscratch to 200, TSM will
stack 2 clients per tape.

So, you ask, "Well doesn't that eliminate the benefit of collocation??!?"
No, it works out fine.
You get 2 clients interleaved on the same tape.
But remember, when you are doing a restore, you don't restore all the data.
Even if you have only 1 client per tape, you still just restore only the
client's active files - TSM has to space over the inactive stuff.
It doesn't really take significantly longer to space over the 2nd clients
data, than to skip over the first client's inactive data.

The big benefit to collocation is eliminating mount and initial search time
on large restores.
Still works, even if you have multiple clients on 1 tape.

************************************************************************
Wanda Prather
The Johns Hopkins Applied Physics Lab
443-778-8769
wanda_prather AT jhuapl DOT edu

"Intelligence has much less practical application than you'd think" -
Scott Adams/Dilbert
************************************************************************






-----Original Message-----
From: Luuk Kleibrink [mailto:luuk_kleibrink AT DELTALLOYD DOT NL]
Sent: Friday, August 16, 2002 5:18 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: IBM vs. Storage Tek


Joni,

You gave the following estimations:

          3590  9840 9940A    LTO
         10 GB 20 GB 60 GB 100 GB
Production
Onsite    1375   689   231    140
Offsite   1600   800   268    161
Total     2975  1489   499    301

Test
Onsite     963   483   163    101
Offsite   1324   664   223    135
Total     2287  1147   386    236

Grand
Total     5262  2636   885    537

And IBM offered a 3-frame 3584. There are some things to consider with
these numbers.
1. Do you use collocation. For your onsite tapes you need at least 1 (often
2, 1 full and 1 filling) for every node or filespace you use collocation
for.
2. Reclamation. Reclaiming 20% of a 10Gb cartridge works very well, but
with 100Gb cartridges this becomes a very long process. We use 3590K
cartridges with E-drives (40Gb capacity) and is is very hard to get a good
tape occupancy. This is especially the case for our offsite tapes because
we sent them offsite every day and therefor they aren't filled up. When we
were using 3490 cartridges we used to reclaim at 50%, now we hardly ever go
below 80%.
3. Offsite cartridges. As I said above, it's very hard to fill offsite
cartriges to capacity. You have to look at your Backup Storagepool
processes. Do you have more than 1 primary storage pool and if so, do you
run Backup Storagepool in parallel or serially. How many Gigabytes do you
sent off daily.
4. Library capacity, with the above numbers 880 slots would be sufficient
because you only have 241 tapes onsite plus your scratch.

We are looking at the option of moving TSM from OS/390 with 3590 to AIX
with LTO. We are now using appx. 500 40Gb tapes and our estimation for LTO
100Gb at the moment is slightly less (say 400-450 tapes) because of the
above mentioned reasons.

All these arguments are valid to a lesser extent for 9940A and 9840. Just
realize that the higher the capacity the lower the usage (percentage wise).

Hope this helps,

Luuk Kleibrink
Delta Lloyd
Netherlands


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