ADSM-L

Re: Expected capacity of 3590 with adsm.

1996-12-30 08:58:44
Subject: Re: Expected capacity of 3590 with adsm.
From: Andy Raibeck <araibeck AT VNET.IBM DOT COM>
Date: Mon, 30 Dec 1996 05:58:44 PST
Peter Zutenis asks:

>I am running ADSM on AIX 4.1.4 and have just installed two 3590's. I am
>currently acheiving a capacity of around 11 G per cart. I was expecting
>to be able to compress a lot more data per cart than what I am getting.

>I have compression on in AIX and also ADSM. The option I used for for
>defining the device class was format=3Ddrive. I am not mixing devices -
>all are 3590. Perhaps I should use format=3D3590C ?

>Am I doing something wrong ?

FORMAT=DRIVE tells ADSM to use the highest format supported by the drive;
in the case of the 3590, it should be the same as saying 3590C.

If you are already compressing the data from the ADSM client, then this is
the most likely explanation as to why you aren't seeing much more compression
from the hardware. If the data is already compressed, then running it through
compression again will most likely achieve little, if any benefit. For example,
suppose you back up 20 GB of data and you use ADSM client compression, getting
a 2:1 compression ratio. The space occupied on tape is thus 10 GB. Although the
hardware can not compress the data further, you are still storing 20 GB for the
price of 10 GB. So you really aren't losing anything.

If you want to test this, try backing up the data with software compression
turned off. If the hardware compression is functioning properly, you should
see higher numbers reported on the capacity.

Andy Raibeck
ADSM Level 2 Support
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