When using this setup as a NAS, isn't your bottleneck the gigabit network from machine to machine? You'll saturate the 1 Gigabit link ( or even 2 Gigabit duplex ) before you can reach 5 Gigabits ( USB3 ) or 6 Gigabits ( PCIe )

I use 2 x 4TB disks in my homeserver, but I keep one online and have a script that brings up the other one periodically and rsyncs everything. This gives me a local backup, something RAID lacks, so I'm protected from fat fingering or accidentally deleting stuff. I also have very minimal downtime, because I can mount that drive in the place of the primary drive in just afew seconds.

I run xfs on the primary drive, and btrfs on the mirror, so I can take snapshots after I rsync and maintain differentials easily.

My point is, you should consider getting rid of RAID and just use the bare drive or LVS Volume.

tkaiser of the armbian project has a lot to say about this stuff. I find his posts in the cnx-software.com comments and armbian forums very helpful.

https://forum.armbian.com/topic/8097-nanopi-m4-performance-a...

https://github.com/ThomasKaiser/Knowledge

ZFS on Linux isn't as memory-efficient as it would be on FreeBSD, which has a much closer file system cache / memory manager architecture to Solaris, but it works fine.

ZFS memory consumption really rockets when you want to use dedupe, which basically wants to store a hash of every block in memory. The sweet spot for its use is in things like multiple VM images - where there's a lot of duplication inside large files that are otherwise different. But there's often ways to structure things to gain back the same space, e.g. with stackable file systems.

Without dedupe, and for a NAS scenario where there isn't going to be a massive working set (typically source or sink for backups, streaming video, etc.), 4G has been more than sufficient for me for years.