using backup with 1/4 inch tape media

[Ken Lerman]

In article <1990Dec31.183601.17768 at magnus.ircc.ohio-state.edu> merrick at magnus.ircc.ohio-state.edu (Tom Merrick) writes:
.I found a couple of unexplained things while using backup at the 3002 level
.and 1/4" low density cartridges (rmt0.4 and rmt0.5).
.
.First, I wrote a tape label using dd, forward spaced over it, then did a
.backup to the cartridge.  I got a write error stating that I had defective
.media.
.
.Second, I did several backups to the same tape cartridge (w/o a tape label).
.Everything finished correctly, so I did a tcopy on the tape and found out that
.my 60 MB cartridge had almost 112 MB on it!
.
.Is backup ignoring the hardware and always writing high density?  This would
.explain both problems above.
.
.Tom Merrick
.Ohio State University

My understanding of these devices is that while the high capacity
devices can read both high and low capacity tapes, they can only write
high capacity tapes.  The capacity is determined by the number of
tracks which the drive writes.  Since the high capacity drives have a
narrower head, there is no way for them to write the wide tracks
required to write in low capacity mode.

Ken