As promised, here are changes to the file server kernel to permit the
use of jukeboxes with different-sized discs on a single file server.
I've tested it with an HP 80EX with 5.2GB discs and an HP 40FX with
2.6GB discs on one file server.

I've enclosed the diffs (a little over 200 lines) and a bundle of the
changed files.  I've done a little other file server work, including
incorporating nigel's/forsyth's wormcopy, since I last synced kernels
with nemo, but I don't think these changes will be hard to integrate.
The files in the fs directory are the prototypes for cloning file
server kernels.