I can't answer your questions exactly, but this may help you figure it out:
The TSM server records the number of bytes it receives from the client, and
the number of bytes it sends to the tape drive.
That is all it knows. It doesn't know how many bytes the the data
represented before the client compressed it. Nor does it know that the
tape drive is doing compression. I just knows how much data it received
across the network, and how much it sent to the drive before the drive
signalled back end-of-tape.
If your clients are doing compression, the server only records how many
bytes it received. Forever after, you will get only that information back
form server queries. So if a client compresses 10 GB down to 5 GB, the
server will say it received 5 GB. If you do a Q OCCUPANCY, you will see 5
GB.
Data that is compressed by the client will not compress much more when
processed by hardware compression. (In fact it can re-expand a little bit,
but I've never seen it do significant harm). So if TSM sends 5 GB of
already-compressed data to the tape, it will take about 5 GB on the tape.
SO, the result, if your clients are all compressing the data, the "capacity"
figures you will see for your TSM tapes will be close to the raw capacity of
the media.
Hope that helps...
************************************************************************
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: Jens Fornfeist [mailto:jens_fornfeist AT IDG DOT DE]
Sent: Thursday, August 08, 2002 6:24 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: A lot of questions concerning encryption and compression !!!
Hi tsm'ers,
we have a problem with the capacity of dlt-tapes. Normally on one dlt-tape
(35gb) you
can store about 50 GB with compression. Our DLT-Library stores only about
30 GB !!!!
So we searched for a compression-switch, but without success. The library
says, that
compression is on. We are using the tsm-encryption-feature for all files on
every client.
The tsm-client-release ist TSM V5.5.1 for Linux on most clients, our Server
is TSM 4.1.3
on Windows NT.
Questions:
1. Does TSM (DES) encryption increase file size and if so, with which
factor ??
or
2. Does TSM (DES) encryption change the file-structure in a way that makes
the dlt hardware compression
uneffective ??
3. Is it in this situation useful to enable the tsm-ba-client-compression
???
4. If encryption and ba-client-compression is enabled => which of this
options comes first ?!?!
5. Do a lot of very small files shrink the tape capacity (because of gaps
on the tape)????
6. Does the volume-capacity shown on the tsm-server represents the real
stored bytes or is it the
summarized value of all stored files given by the tsm-client-nodes
(before or after encryption???) ?
Thanks for help!
Mit freundlichen Grüßen
Jens Fornfeist
----------------------------------------------------------------------------
----
IDG mbH, Cologne
----------------------------------------------------------------------------
----
|
