[kwlug-disc] TrueNAS scale (4-5 drive configuration)

[bob at sosc.ca]

> Note with TrueNAS: Unlike with mdadm, lvm, or btrfs, you're stuck with
> the layout you pick. So if you have a 5-drive RAIDz1, you can't just add
> a drive to bump your capacity (ex: migrate to 6-drive RAIDz1). This
> functionality is reportedly "coming soon", ...

This is why I think doing RAID1 vdevs into a pool is a decent idea. 

I've tested this setup on a skunkworks host* and I was able to add and remove vdevs to the pool (with appropriate waiting for rebalancing of the used blocks).

The benefit to this is you can mix and match disk sizes (albeit in pairs) and grow/change the pool 2 disks at a time instead of whatever you've committed to your z1 or z2 vdev. And your rebuild is less stressful because you are only mirroring a single disk (debate welcome on that one, I am not entirely convinced).

The downside is if the wrong two disks fail, your whole pool is pooched because it is effectively a RAID0 of RAID1 vdevs.

Discussion welcome on this.

Bob.

* skunkworks host I just realized as I was typing this the seems to have become "homelab prod" (facepalm).