using rdump with 1/4 inch tape media

using rdump with 1/4 inch tape media

Post by Dale Hubl » Thu, 03 Jan 1991 23:04:32



      Does anybody have an answer for an rdump question I have?  I tried to
use rdump to backup a user's /u filesystem to a QIC 150 tape drive on our
server (520).  If I take the drive to the workstation I wish to backup,
I can easily backup the 75 Meg onto one DC600 cartridge (in QIC 120
format).  The same 75 Meg requires 4 cartridges when I use rdump to
backup across the network.  The documentation refers to the -b option
on the rdump command but does not give a default value.  I am backing
up to /dev/rmt0.6.  Does anybody know what blocking factor will allow
me to write in a QIC 120 format using rdump?

Thanks in advance for any help!
Dale Hubler

--

 
 
 

1. using rdump with 1/4 inch tape media

 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

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