IBM x3630 spontaneously reboots

[Ivan Voras]

I have an IBM x3630 server with a LSI 2808-based controller (IBM
MegaRAID-branded M5010) which spontaneously reboots at random
intervals of 5-10 hours. It runs NAS4FREE based on 9.1-RELEASE, and it
looks like I either cannot get kernel dumps out of it, or there are
not panics; since the machine doesn't "pause" on panic I think it may
be the latter, but since the machine boots from an USB flash drive it
may be that it cannot write the kernel dump to the drive. The server's
main storage is used with ZFS.

I cannot provoke it to reboot, it doesn't appear to be related to
loads, network or disk IO activity. Any ideas?