Hanging PowerEdge 1850

[Mark Davies <mark%ecs.vuw.ac.nz@localhost>]

Hi,
   I have a newly setup Dell PowerEdge 1850 running 6.1_STABLE/amd64 
from a few days ago that will hang completely if I just copy a 20GB 
file (or similar sized groups of files) around the filesystem.  Stops 
responding on the console, stops answering pings.  This machine (or 
most parts of it) was happily running 6.x/amd64 a few months ago.

I'm after suggestions of how I can pin down whats actually failing, be 
it hardware or some software issue.

cheers
mark