Buffalo DriveStation Duo User Manual page 4

Using the RAID Utility
The RAID Utility allows you to configure your DriveStation Duo in
several modes:
Independent Disks - Appears to your computer as two separate hard
drives.
Spanning Mode - Appears to your computer as one large hard drive.
RAID 1 Mirror - Appears to your computer as a single drive. The
second drive is an exact copy of the first drive, for redundancy.
Note that changing the mode of the drives in your Duo will erase all data
on them! Back up any important data before using the RAID utility.
You may launch the RAID Utility by clicking on RAID Setup Utility in the
HD-WIU2 program group.
Or, you can launch the program from the Start menu: