Senitrus believes in the concept of keeping your files on another drive that does not have your OS and applications on it. If something was to happen where you had to reformat your computer, or if you would want to have two OS?es on the same machine (why?), then the personal files on a second drive starts to make sense. In addition it is much easier to back up an entire drive rather than backing up folders or doing complete images hoping to get everything.
The NL series will have 2 SSF (Solid State Flash) modules soldered on the motherboard. Each module can range from 256GB? to 4TB? is storage capacity. The NS Series can only go up to 1TB. This is not to favor the NL, but again you need a place to put all of this on a motherboard. Unless there was a single 8TB SSF chip, then there likely is no way to give the option for 8TB to the NS Series. While some people might question for the concern of supporting 2TB on the smaller, and 8TB for the larger, keep in mind that there will be two different physical drives. With that said, I will can only use half of the chips needed for the higher capacities.
You can choose to have a different capacities. For example, your OS drive might be 512GB, and your personal files drive might be 1TB. If you wish to use RAID-1, then both drives must be the same capacity. You would also likely have to use your microSD card for storing personal files. During setup, Senitrus will advise against storing your personal files on the OS drive.