Local RAID vs NAS - hard drive upgrade, options

Hey gang. Hoping to gather some input and suggestions here…

Exhibit A: I currently have a nicely-equipped desktop tower which I built and has a small SSD for my Windows C-drive and a 3TB HDD for my Data D-drive. PMS runs on this desktop and all of my media (movies, TV, music, photos) is on that 3TB drive. I’m currently down to less than 1TB of free space and I foresee running out of room on that D-drive within the year.

Exhibit B: I have an older 2-bay Netgear ReadyNAS Ultra 2 Plus, currently running two 2TB drives. This is being used for misc non-media files but not currently being leveraged for my Plex environment. But it could be.

Exhibit C: I also have an older 2-bay Seagate BlackArmor NAS, currently running two 3TB drives. This is currently serving as my Plex backup unit. I run a piece of software on my desktop PC called “DropIt” and it monitors my Plex media folders, once an hour copying any new files it finds there over to this Seagate NAS.

Here’s my dilemma… I will soon have more than 3TB of media. What is the most effective upgrade path given my hardware?

My goals/limitations are these:

  1. 6+ TB of storage capacity
  2. A local (i.e. non-cloud) backup of my Plex media files (family photos, music collection, movie MKV files - I really don’t want to re-rip and re-compress my library if I can avoid it. It’s taken a while!) I’d like to maintain at least 2 copies locally of each file, on separate hard drives.
  3. Centralized repository for media files and documents, so all laptops and devices in the house can save to one central repo INSTEAD of saving locally to our myriad devices. (“Which machine did I download that PDF? Where is that picture I took?”)

Some questions I’m wrestling with: Do I add a 6TB E-drive to my desktop, replace its 3TB D-drive with a 6TB drive, and set up local RAID 1 array? Do I instead just add more drive(s) to my desktop and start playing with Drive Pool or Drive Bender? Do I upgrade the drives in NAS B or NAS C and start pointing PMS at the NAS instead of the local desktop HDD? None of the above?

Thanks in advance for any input and recommendations!!

Any thoughts, gang?