ok, I understand...
Well, it depends on the brand of the RAID. Ussualy, if a disk drive is fault, ou just need to replace it, how to do it? again, it depends on the hardware, if it is hot swap, you can replace it online and (normally) the hardware RAID will rebuild all data.
You *must* read the hardware documentation. Some RAID controllers need to rebuild data manually, others are automatically.
Cheers.