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From: kaiser@ananke.stgt.sub.org (Andreas Kaiser)
Newsgroups: comp.unix.aix
Subject: Re: using rdump with 1/4 inch tape media
Message-ID: <50.2786E262@ananke.stgt.sub.org>
Date: 6 Jan 91 08:33:16 GMT
Organization: Ananke, Stuttgart, FRG
Lines: 17


 DH> I can easily backup the 75 Meg onto one DC600 cartridge (in QIC 120
 DH> format).  The same 75 Meg requires 4 cartridges when I use rdump to
 DH> backup across the network.

If you backup on a local tape, the tape will most likely be operated in the 
"streaming mode", where there is little or no stop-and-go. When operated via 
network, the tape data rate might be about as high as the network data rate 
(measured with ftp on an idle 4Mbit token ring). So the tape operates in 
stop-and-go mode, significantly reducing its capacity. In the manual of the 
tape, there is a picture saying the capacity is reduced from 150 MB to 30 MB 
when operated in non-streaming mode. I personally have trouble believing this 
relation, especially at large block sizes, but its given in IBM's docs...

        Andreas