I tried Ubuntu 10.10 RC today, which has a newer kernel, but with no luck. Actually, it was even worse, reporting IO errors on boot. Looks like the mpt2sas driver isn't reliable for all hardware yet. I just installed Windows 7 and I have yet to experience any similar problems here.
I recently bought a new file server setup consisting of a SM 846E16 case and a SM X8SI6-F MB (with LSI 2008 SAS controller on board).
I have installed Debian Squeeze (to get the mpt2sas driver), but the system is extremely slow during startup (5 min or so), and I keep getting some mpt2sas...