Halt goes into uninterruptable state while shutting down - how can I shut down?

I have had a hard drive failure which has caused a lot of processes to go into an uninterruptable state ("D" state in ps- See this question). I cannot kill these processes, so I wish to shut down, but unfortunately halt is also now showing as "D" and the machine will not restart!

ben@jack:~$ ps aux | grep "halt"
root      7875  0.0  0.0   4148   700 ?        S    Mar08   0:00 /bin/sh /etc/rc0.d/S01halt stop
root      7880  0.0  0.0  10436   680 ?        D    Mar08   0:00 halt -d -f -i -p

How can I recover from this?

If your system has it enabled, you can probably use Magic SysRq to force a shutdown or reboot. Otherwise hopefully you have a network-accessible power supply you can log into? Then you can power-cycle the outlet the host is connected to.

Or maybe you have iLO or ipmi on the box, and you can log in to one of those to force a power cycle?

And of course as a last resort, it's time to send a flunky onsite.