OS X 10.3.5 Server 5.5.4 on a G4/800.
110 db's totalling 1.07 GB.
15 users.
Software update and date/time update off.
No file sharing and no open external ports.
Server app crashed during a backup to an external firewire drive. Server config claimed the server was running but users could not connect. We instructed server to stop - finally pulled the plug [rebooted] after 120 minutes. Db's were all crashed. So went to backups.
Are there known issues with backups to external devices? It is a Maxtor 40GB. The Finder hung into infinite pizza-wheel-of-death when we tried to open a folder on the Maxtor drive. Seems a likely suspect.

from the Event Log..

Sep 29 12:15:33 FMServer.local INFO: Cache flush completed.
Sep 29 12:20:56 FMServer.local INFO: Schedule IntDyn20MTWRF waiting to run.
Sep 29 12:20:56 FMServer.local INFO: Schedule IntDyn20MTWRF running.
Sep 29 12:21:20 FMServer.local INFO: Schedule IntDyn20MTWRF completed.
Sep 29 12:30:33 FMServer.local INFO: Cache flush completed.
Sep 29 12:30:56 FMServer.local INFO: Schedule ExtDynNoonMTWRF waiting to run.
Sep 29 12:30:56 FMServer.local INFO: Schedule ExtDynNoonMTWRF running.
Sep 29 15:48:26 FMServer.local INFO: Schedule ExtDynNoonMTWRF completed.
Sep 29 15:48:26 FMServer.local INFO: Cache flush completed.

Note that ExtDynNoonMTWRF took 3 hours 11 minutes 30 seconds to run. Though I supose it really didn't as the backup was incomplete.
It backs up the same db's as IntDyn20MTWRF which took 0 hours 0 minutes 26 seconds.
Ext[blah] does write to the external Firewire drive.
The 12:20 backups were good.
All the running db's were crashed.

In the absence of anything else we have decided to replace the external drive and increase our supplies of eye-of-newt and ant whistles.