I am wondering if this is a "quirk".  I have a fairly old QIC-150 drive
(from when they stenciled "150MB" onto them because most drives weren't),
and I get
Jan 11 11:49:01 taniemarie /netbsd: st0(ahsc0:4:0): illegal request, data = 00 0
Jan 11 11:49:01 taniemarie /netbsd: st0: cannot set selected mode
Jan 11 11:49:02 taniemarie /netbsd: st0: bad request, must be between 0 and 512

(Unfortunately, that 1st message, all 0's, is truncated by my display this
week)

... but only the first time I try to write the tape.  A 2nd try works, with
no special errors or warnings.

In other news:  Does anyone else see 'tar [tx]b' dump core consistently?
I'll be looking at this, but it's sort of disturbing.

-s