This issue was observed using MacOS 8.1, but likely applies to other versions as well.

When the Mac starts the reboot process, it will send a Flush command to RaSCSI that is not supported. This causes RaSCSI to immediately crash and will cause the Mac to freeze (before it reboots).

To recover from this situation, you need to re-start RaSCSI.

Received an invalid flush command 15!!!!!
rascsi: disk.cpp:7864: void SASIDEV::FlushUnit(): Assertion `0' failed.
make: *** [Makefile:108: run] Aborted