When you create a RAID 1 array, the system will ask you to select one of the rebuilding options. When you create a RAID 0/1 array, the system will make the initialization automatically for you):
1. Initialize: Clear all data of the original disk and the mirror disk.
2. Synchronize: Copy all data of the original disk to the mirror disk
Also, you can select synchronizing from the menu.
Note:
Only RAID 1 and RAID 0/1 can be synchronized.