I wrote a program awhile back called "vol".  It's similar to a program
by the same name that came with Minix, but I wrote it from scratch in
C.  You use it like this.  To backup:

tar ... | compress | vol -w /dev/fd0 1440

and to restore:

vol -r /dev/fd0 1440 | zcat | tar ...

It stops and prompts every 1440 (or whatever) Kilobytes and asks you to
place the next disk in.  Is anybody interested in this?  Please respond
via e-mail.  If there are enough responses I'll beef up it's error
checking and offer it "officially" as a new binary.

Probably what we really need is a dd(1) with a "pause" option.