How to install drives with different capacities in the NT2 U3?
When you install drives with different capacities, always install the smaller drive in slot A and the large drive in slot B for best performance.
Keep in mind that when not using Non-RAID, the total size of the volume will depend on the drive with the smallest capacity. As an example, when using RAID 1 with a 1TB and a 2TB drive, the available storage capacity is 1TB (a bit less after formatting). In the same example with RAID 0, the available storage capacity is 2TB and not 3TB.