I have a NW 6.5 server with a 14G volume with 13G worth of data. I am
running BStor 11.1 sp3 and have 20G tapes. About the middle of last
week I start getting a message asking for a second tape to continue the
backup because the tape is full. This is an established server with an
established backup routine where nothing (in principle) has changed in
a looong time.

Any ideas?