MD3000 replacement disk

Hello all. Straight to the point I was Supplied with a MD3000 server and told have at it. Being completely green to the server I managed to stumble through the set up and have be using the unit for three years. After a internal power problem with my office the units kept restarting and (my understanding) damaged the disk. The information can not be access through the server. Disk group went unavailable. I do have a raid on this disk group. Unfortunately I can not remember what disk was the mirror. I pulled the disk and set it a side and purchased a new disk. I am really at the end trying to figure out and try to reactivate the disk. can someone help and fellow to trying to get this server back up to where it was