"rdump" only writes half as much data as "backup"

[Chuck Henkel]

Context: Two RS/6000 Model 320s running 3001.
	 Tape drive configured for 512 byte blocks, no ECC

I'm trying to use rdump to back up a filesystem on "rs1" to a
cartridge tape on "rs2":

rdump -0 -c -f rs2:/dev/rmt0.4 /u

only writes about 10 meg on the tape, then asks for another. If I use
a high density tape, (3M 6150, /dev/rmt0), it only puts about 20 meg
on the tape, then asks for another.

The "-b" flag (blocksize) has no apparent effect. Backing up
filesystems on rs2 (the machine with the tape) works fine.

What's the deal?

And, why doesn't this work:

backup -0 -b 126 -f - /u | rsh rs2 dd of=/dev/rmt0 obs=126

The dd dies immediately with "invalid argument to system call" or
somesuch. In fact, I can't get dd to write on the tape at all.

--
| Chuck Henkel                      |                           |
| Department of Nuclear Engineering | Support nuclear power.    |
| N.C. State University             |                           |
| henkel%nepjt at ncsuvx.ncsu.edu      |                           |