1) My 8950 / 2TB NVMe hard drive is Western Digital Black 810 NVMe 2) You can buy any hard drive you want - SATA, SSD or NVMe. Either one will work. If you'd like a full discussion on price vs performance vs reliability there are entire forums dedicated for that. Google is your friend. 3) Backup, Backup and Backup again.     
I ordered an XPS 8950 with the 2TB NVMe SSD boot drive, and have three questions: 1) What is the actual manufacturer/model of the SSD it comes with? 2) If I want to add a second 2TB SSD to store data, what should I buy? (priorities are reliability, performance, energy efficiency, and cost, in that order) 3) Longer term, what are recommended ways to protect against drive failure?   My current scheme is to keep images of the system on external backup drives (refreshed occasionally) and use a combination of dropbox (real time), a  cloud backup service (daily), and File History backing up all my data files to the external drive(s) (hourly).   I figure with that I don't need RAID, but am I missing something or screwing up the performance of my system? Thanks for any and all advice!  
XPS 8950, SSD questions