D-Link DNS-327L User Manual page 53

Section 3 - Installation
Step 35 - Under RAID Configuration, Select RAID Type, choose
RAID 1. Read the RAID 1 configuration requirements.
Click Next to continue.
Step 36 - With RAID 1, the drives are mirrored for redundancy. Map
Drive to Network indicates that the NAS has separated the drive
into a RAID array.
Note: If the size of these two drives are different, the spare drive
space will be formatted as JBOD Volume.
Click Next to continue.
DNS-327L 48
D-Link ShareCenter User Manual