NEC Express5800/R120b-2 User Manual page 280

IMPORTANT:
If the server is turned off during rebuild processing,
the processing is stopped. Restart the server, mount the new hard disk
drive in hot swap mode, and then perform rebuild processing again.
Observe the following notes on using the auto-rebuild function.
Do not turn the power off or reboot the system during rebuild
processing.
Let 90 seconds or more pass between removing a failing hard disk
drive and mounting a new one.
Do not replace a failing hard disk drive while rebuild processing is
being performed on another hard disk drive.
Troubleshooting 8-7