When one of the two hard drives has been taken out of the RAID System under RAID 1 mode and updated elsewhere, the existing RAID set for the non-updated hard drive (Target Disk) needs to be deleted before the updated hard drive (Source Disk) can be placed back to into the RAID System.


After the deletion, the updated hard drive (Source Disk) can be placed back into the RAID System while the RAID System is powered on. Then, configure the Rebuild process by selecting the non-updated hard drive (Target Disk) as the Disk to Rebuild onto from the updated hard drive (Source Disk) and choose RAID 1 mode. By following these simple steps, the Rebuild process should complete correctly.