My son set me up with a NAS device running the freenas operating system( no affiliation).
https://www.freenas.org
Much faster than any commercially available 1 or 2 drive systems. I store and stream all of my media from this one NAS system.
My NAS has four 4Tb drives in a RAID5 configuration. In this manner I can loose one drive, replace it and reconstruct the entire data set from the surviving three. If one drive dies, the NAS will still operate (risky) until the failed drive is replaced. Other configurations are available to provide additional protection and security.
In the three years I've had this NAS I've lost 2 drives (separate events) without losing any portion of my dataset. Freenas is very configurable and supports SMART, which sends me emails once a drive begins to show symptoms of failure. I get a notification, identify and replace the failing drive and the operating system rebuilds the dataset from the 3 surviving drives.
My system is housed in a standard computer tower with a power supply big enough to accommodate 4 drives. The operating system (Freenas) runs from a small USB memory stick.
Freenas can be programmed to perform self diagnostic tests as I see fit.
I like the safety, the ability to expand and the speed.
My son did a smart thing when he built my NAS, he sourced the 4 drives from different vendors in case one batch proved faulty.
(I will not use Seagate again).
Freenas isn't as "Plug and Play" or simple as the inexpensive NAS boxes you see at Best Buy because it's so much more. It's bigger, faster, safer and more configurable. Any questions are addressed in the online user's manual and there is a user's forum.