>>Backups seem to be hanging on some files (often, but not always,
large ones), and the server times out after 300 seconds, dropping the
connection. <<

Arian,
Your problem sounds identical to what we have with Netware 4.1
We have been experiencing the same problem and have been working to get
it resolved for over two months!        We can circumvent the problem by using a
high value for COMMTIMEOUT like 3600, but performance is intolerable!

It takes about 5 hours to backup 1 gig!!
We have observed "waits" as long as 15 minutes using the QUERY SESS
command during the backup.

Please let us know if you find anything out.  (we will do likewise)

Mike Martin
Baptist Health System of East Tennessee
mmartin AT bhset DOT org