Ever since the upgrade from 5.1 to 6.5, our Dell Poweredge 2600 has been
having performance problems. What happens is that it performs just fine
and then, after a week or so up, starts slowing down when it's being hit
by many users. The CPU utilization goes up to around 90% and just sits
there, the server is slow responding, even to changing console screens,
and any attempt to access or look at files on the server via a client is
diabolically slow. The CPU goes down again eventually when it's less
busy, but it just keeps getting slower when under even moderate strain.
Rebooting seems to cure this, at least for a week or two.

Server specs:
Dell PE 2600, HT disabled in BIOS, using a PERC4Di RAID controller, with
the latest firmware applied, and the latest BIOS firmware on the server
itself. Running 6.5 SP4a, volumes still all TFS, 2 GB RAM.

Any tips as to where I should be looking? The busiest threads when this
high utilization occurs are "servernn" type threads. Oh, I've also not
loaded CIFS or AFP...

At the moment, I have no idea where to look, but dang this thing is
behaving worse than a Windows server.