Posting here before filing a bug in case this rings a bell...
Dell PowerEdge 2900, with PERC 5 "integrated" controller. All BIOSes and firmware levels up to date as of ~6 months ago. (Which should be pretty current, since this isn't a new system!)
Copying install55.fs to a USB stick and booting from it starts to boot, gets part-way through the boot process, then suddenly reboots.
This server does the exact same thing with Ubuntu 12.04.x, but otherwise works fine: FreeBSD (via FreeNAS), DragonflyBSD 3.8.2, Debian (via ProxmoxVE), CentOS 6.4 all boot and work just fine; it's been operating as a Proxmox server in production for the last 12 months without any issues, so I'm fairly confident it's not a hardware problem.
I don't even know where to start with this... ideas? Right now, I'm re-writing the install FS so I can re-test, then I'll try an actual CD-ROM. I can take video of the boot screen, not sure how to get serial console output that early in the process.
-- -Adam Thompson [email protected]

