It is 2, 8 TB drives. You can setup through the software in Raid 0 which will show on your PC as a single 16TB drive, or Raid 1, which mirrors the drives (shows as one 8 TB drive on your PC) and makes the drives exact duplicates so if one fails, you replace it and it will re mirror from the other good drive. Raid 0 good for space, Raid 1 great for backing up photos and anything else you absolutely do not want to lose if a drive fails.