Couple questions regarding VDEV setup and which RAIDZ configuration to use

[LiquidAurum]

I just got my FreeNAS up and running and I just realized I still have a couple questions left. So to my understanding if you lose one VDEV the entire pool is lost. So for my setup I have 4x4TB Hard drives so I put them all into one VDEV and created a pool out of the one VDEV. That sounds fine right?

Also I created with RAIDZ-2 and I only have 6.8 TB usable space. That's basically half of my raw storage, I thought only mirroring drives took half the raw storage. So I'm looking into going RAIDZ instead. Would that be a bad idea?
BTW this is just for hosting plex, tautili, syncthing/resilio, teamspeak (possibly)

 

[sretalla]

So for my setup I have 4x4TB Hard drives so I put them all into one VDEV and created a pool out of the one VDEV. That sounds fine right?

Sure

So I'm looking into going RAIDZ instead. Would that be a bad idea?

Maybe... RAIDZ1 is not recommended for drives over 2TB due to the potentially long resilver time in the case of failure and the fact that you run without redundancy while that (high-stress task) happens on your remaining disks.
If you don't love your data so much, then RAIDZ1 may cover your use case (where you're prepared to lose it all to have more space when things are fine and you are lucky).

 

[JaimieV]

RAIDZ2 gives you two-drive redundancy - which means two drives can fall out without losing data.

If you have four disks, the only way to have that level of redundancy is that two disks-worth of data across the whole array is redundant. So yes, half your RAID is redundant data, and you get the same free space as if you were using mirrors. You do get more safety though, as any two drives can drop out without damage.

If you had 5 disks in RAIDZ2, you'd get 3 disks of usable space. 6 disks, 4 disks worth of space.