I set up the QNAS NAS that my brother gave me (he upgraded and gave it to me after my Drobo died). First I had it with 6 4-TB hard drives because I didn't have enough 14-TB or 8-TB hard drives. But that only gives me 16.9 TB space and it turns out you can't reduce the number of drives in a RAID set -- you have to delete the RAID set and create a new one. So now I'm thinking:

RAID 5 Set 1 - 6 TB, two 8 TB (leaving me with one 8 TB spare) = 12 TB
RAID 5 Set 2 - three 14 TB (with one 14 TB spare) = 28 TB

I lose a bit of space with Set 1 but I don't have a fourth 8 TB drive and if the 6 TB dies when I replace it Set 1 will automatically start using the extra space. Set 1 would also have the QTS software installs.

Plan:

1. Change MBP M4 Time Machine backups to two WD EasyStore HDs. This frees up the 6 TB and 8 TB drives I've been using.
2. Move data off one 14 TB drive -- I have them as two 2-drive mirrored sets so I don't need to move off the other one yet
3. Redo NAS
4. Move data onto NAS
5. Backup NAS data to 4 TB drives -- I like to have one backup that I update weekly or monthly in case of catastrophic NAS failure