The x8 drive was designed with two drives and two controllers inside. Each controller manages a half section of the SSD; so, it shows two separate drives that can be configured as RAID 0 to reach the whole capacity.
Other models described are x4 come as one full drive of 6.4TB, meaning that it comes as one full drive using one controller:
These drives will be recognized as two separate SSD storage units of 3.2TB each:
Theoretically, RAID configurations are possible between both portions of a P4608/P4618, meaning that RAID-0 can be used to combine them and use full capacity. RAID-1 can be used for fault tolerance (but will not protect in case of complete drive failure). This also applies to RAID configurations involving other drives, such as a RAID-10 configuration between two P4608/P4618.
Contact Solidigm™ Customer Support.