Created on: May 24, 2013
Last updated: August 25, 2015
For standard RAID 5 mode (using all four drives), the total capacity will be as large as 3 drives. For example if you are using four 1TB drives the useable capacity would be 3TB.
USB 2.0 VERSION ONLY:
When Mode 9 (RAID 5: 3 Drives + Spare) is used, the total capacity will be only as large as two drives. When one drive fails, the data will be rebuilt immediately by using the spare drive, rather than waiting for the faulty drive to be replaced.