The system should only need to rebuild if one of the drives fails. If both drives are working, no rebuild should be needed (although some RAID controllers might periodically do a run through all the blocks on the drives to compare them as a safety measure).
Thanks. I hope after this rebuild, the mirror operation will be performed at the same time that a file is read to the first drive - and only to update the change. I can't see myself going through this again. I am new to Raid as you could see. With a Raid 1 system, if I delete a file or write a file, does the change on the mirror drive happen in parallel instead of a rebuild??