I currently have a Qnap NAS with mirrored 8TB drives. I want to build my own NAS to upgrade my storage, using TrueNAS scale 24.10. My desire right now is to get 3 8TB drives for the new system (2 storage + 1 parity), copy my data from the current NAS to the new system, then add the 2 older 8TB drives to the new system so I have 4 8TB storage drives with 1 parity drive all seen on the LAN as one drive. I have done a lot of searching, but had conflicting/confusing answers as to whether this is possible.
My question is… is this possible? Or is there a better way to do what I am thinking of doing?
Yes. Well, mostly. No modern RAID has a dedicated parity drive; in any modern parity RAID (RAID4, RAID5, RAIDZ), parity is striped across all drives in the array. But the gist of what you’re wanting to do is possible.
In one word, you want to do raidz vdev expansion. (OK that’s more like three words.)
Note that, if you can afford it, raidz2 (double parity) is recommended over raidz1 for drives of this size.