RemoveFromRAID – Correct syntax

I have an Xserve G5, it has been configured with a mirrored raid array and a standby spare, I need to press the standby spare into service as a normal drive. ( I have a spare drive in a caddy and ready to swap out a failed drive in the array) I can see I need to use the RemovefromRAID command, but can't seem to get the sysntax right. Does anyone have a walk through for this. I suppose it is testiment to Apple that this is the first time I have had to use the Terminal window. Many thanks, Steven.