The LaCie 2big Network supports two RAID modes, Big (Concatenation) and Safe 100 (RAID 1).
In Big mode, the two physical disks are combined (concatenation) so that one single yet larger logical volume mounts on the desktop, offering maximum possible capacity (the available capacities of each disk are cumulated). If one physical disk fails, the data of both disks become inaccessible. One Big Volume
Safe 100 (RAID 1)
In Safe 100 mode, the two physical disks are mirrored together (RAID 1) so that one single logical volume mounts on the desktop. All of the data (100%) are saved simultaneously on each disk (the available capacity cannot exceed the available capacity of the lowest-capacity single disk). If one physical disk fails, the data are available immediately on the second disk. When a drive is replaced after a drive failure, a rebuild begins automatically. All data are copied from the existing drive to the new drive. One Safe Volume