FWIW, I replaced SunOS 4.1.3 on one of my sparc IPX's and backups (via  
UMD's amanda utility) have never once coughed.  I use a HP 4mm 2gig DAT  
or an Archive 4mm 2gig plus compression.  I can't recall the exact  
model numbers of either, but the HP was something like 3570A or some  
such.  NetBSD doesn't seem to like older Fujitsu 500mb drives but I  
don't either so I toss them out.  My Sony SDT2000 (4mm DAT) works like  
a charm on my home i486.