Hopefully I am at the right place for this question because it’s not a commercial one:
I am planning to upgrade my home server TrueNas storage to a RAID system and I wanted to collect opinions from people that use this system on a daily basis/in a commercial context. Currently my TrueNas is running basic tasks like a Media server and smaller VMs (mostly 1 or 2 at the time) with Docker.
Next to this my goal is to get rid of OneDrive as my main storage/backup and use my NAS instead, mostly because I want to have easy expanding flexibility.
After watching Toms video about ZFS storage expansion (TrueNAS: How To Expand A ZFS Pool - YouTube), two big questions came up from my side:
- What is this best RAID combination for my scenario (Multimedia/Data NAS) to get ‘daily useable’ transfer speeds considering >1Gbit networking and good reliability?
Over this forum and multiple youtube videos and articles I found that the most common recommendation are mirrored stripes. And also, this table (ZFS Raidz Performance, Capacity and Integrity Comparison @ Calomel.org mentioned in another video from Tom) speaks in favor of RAID 1. But I am very sceptical to rely on the hope that just one drive is going to fail per VDEV, with 2 drives per VDEV in mind. It is private data, so it is not that critical for a business. But for example, I also have nearly 1TB of material from my university on it (with a backup on onedrive) and I plan to keep this data for life - but not Onedive 
Also 3 mirrors per VDEV seem pretty inefficient in my eyes and also too expensive for private use. Could someone still recommend this configuration ? Out of the mentioned table I would choose RaidZ2 with 4 drives to get two possible failures per VDEV. But then I also have two use at least two VDEVs to get better utilization of a network that is faster than 1Gbit right ? It would be nice if someone could give me a suggestion out of personal experience 
My setup currently has just one 4tb Ion Wolf and I wanted to buy a few of these.
- Speaking of just one drive: What is the best migration process when changing the RAID ? I saw that extensions of VDEVs are not possible but in this case, mirroring would be a huge advantage. Can’t I just clone my first disc to a second to get the first mirrored VDEV and then simply add a second one ? Or is this the typcial “not the way how ZFS works” ? So maybe the RAIDZ2 I already was looking for ?
→ set up the first VDEV → copy files from current disk → setup second VDEV and include the old formatted disk, would that be possible ?
Every answer from an experienced user is appreciated.
Also I have to excuse any possible mistakes or technical misunderstandings from my side.
Thanks in advance 