Is there a way to make rdump to Exabyte faster?

[Caroline Lambert]

I have one Mountain FileSafe Exabyte on a DEC5000 which I use to backup
several Decs and Suns. It takes three times as long to back up 1GB on
a remote Dec as it does a remote Sun. This is becoming a problem since
there is a very small time gap between when the grad students go home
at night and when more 'normal' people come in in the morning, and the
amount of disk used is growing.

So my question is: what parameters can I use to make the backup 
		   go faster?

This is what I use to back up a Sun:
rdump 0usdbf 54000 6000 20 tapemachine:/dev/nrmt0h /filesystem

The logic behind this is that tape density is 6000 bpi, the 54000 is
the factor needed to get the right tape size, and the blocking factor
is 20 because that's the most the network can handle.

Doing a remote dump from a DEC5000 (Ultrix 4.1) I am using the 
parameters recommended by the manufacturer of the tape drive, 
for lack of anything better (there's no 'b' parameter for the ultrix rdump).
This is for a 2GB tape:
rdump 0unsdBf 346 4137733 2097152 tapemachine:/dev/nrmt0h /filesystem

which don't make very much sense at all - I thought the tape density was
6000 bpi. The backup is reasonably fast
on the machine the tape drive is on, but much slower (3-4x) for the remote
Decs. Monkeying around with the size and density doesn't make any
difference (which makes sense since I gather the machine is supposed
to be smart enough to read the density off the tape anyway).

Any ideas beyond switching the tape drive from one machine to another?
What does the 'o' argument to rdump do (the man page is
uninformative)?

--
Caroline Lambert               
Dept. of Geophysics
Stanford University	caroline at pangea.Stanford.EDU   standard disclaimer