Was this a replacement for a dead drive, or are you trying to add more space to the array?
If the former, beware of mirroring. Sometimes when a drive starts to go bad it can cause a mirror to wipe the data from the good drives. If the system didn't integrate the replacement drive seamlessley it is most likely because of this, and you will need to reinstall and restore from backup.
If the latter, you can't just add space to an array plug-and-play. You will need to re-install for the larger array and restore from backup.