tar and Exabyte under Ultrix

[Don Kossman]

we have an Exabyte 8mm cartridge drive, with the Q-bus
controller distributed by Contemporary Cybernetics, installed
in a MicroVAX-II running Ultrix 3.0.  We just had the
drive upgraded to the latest ROM level.

we use it for dumps, which work just fine, and have used
it with tar as well, but only with the "c" option (ie create
a new archive).  when i use the tar "r" option (ie append to
the end of the archive), however, i get an "error 0,
writing to archive 1".  the exact same operation works just
fine with my TK50 and TU81-plus...

i spoke to the vendor, and the tech support person thought he'd
seen a  similar problem in the past with tar and said that he'd check,
but sort of thought that "tar r just doesn't work".

meanwhile, i thought i'd ask the net....
has anybody seen this or something similar?  IS THERE A WORKAROUND?
(We don't have Ultrix source)

TIA for any pointers or info.
-- 
Don Kossman, SEI Information Technology, Los Angeles
  ...sun!tsunami!seila!don, -OR- mahendo.jpl.nasa.gov!jplgodo!seila!don