Is it possible to have a pool with different mirror vdevs (Mirror, Mirror 3) and sizes?

[u6f6o]

I am currently in midst of building my first home nas solution with freenas. Lately I stumbled over this article, that basically suggests to use mirrors instead of RAIDZ variants for home nas solutions.

While I don't want to argue if this can be seen as a general recommendation or not, I found one aspect of mirroring quite suitable for my build. So far my biggest problem was to find out how much space I gonna need in 3 years from now. Atm., required space is very low (<=1,5TB), as I intend to use my nas primarily for backing up my Mac Book, PLEX media server and storing photos, this requirement can change rather quickly.

If I understand correctly, using RAIDZ2, I'd have to add the exact same amount of disks and space again as soon as I want to expand as a second vdev or alternatively replace each and every single disk with a larger one.

Using mirrors instead, I could add another 2 or 3 disks mirror as long as I have SATA ports left.

Now back to my question (hoping that my assumptions so far are correct)... In case I go with the mirror solution, is it possible/recommended to add another vdev with a different mirror type, lets say mirror 2 instead of mirror 3 and probably different size?

My train of thought is the following: I would start with a Mirror 3, 3 x 6 TB, which would give me 4,5 TB usable data space. In case I need more space, I could think about adding another Mirror 2, 2 x 5 TB and put lesser important data there, while keeping my important stuff on the Mirror 3.

As I am quite new to freenas but eager to learn, please be patient in case I messed sth. up completely

 

[UdoB]

Now back to my question (hoping that my assumptions so far are correct)... In case I go with the mirror solution, is it possible/recommended to add another vdev with a different mirror type, lets say mirror 2 instead of mirror 3 and probably different size?

Yes.

Having the same type of vdevs is not a strict technical requirement but it is highly recommended. If you mix them up you might get "hickups" in performance depending on which vdev you are actually using when accessing a specific file. The expected speed drops down to the slowest vdev. IOPS increase to the sum of all vdevs.

In case I need more space, I could think about adding another Mirror 2, 2 x 5 TB and put lesser important data there, while keeping my important stuff on the Mirror 3.

NO!

You can not control on which of the vdevs your important gets stored. All vdevs of one single pool are striped.

You would need to add those additional drives as a new, independent pool. Usually this is not what you want as it complicates data management: you need to setup replication and other tasks once more.

Best regards

 

[Robert Trevellyan]

In case I need more space, I could think about adding another Mirror 2, 2 x 5 TB and put lesser important data there, while keeping my important stuff on the Mirror 3

You can do this if you set up the two new disks as a separate pool. Most people like to have all their storage in one pool, but it isn't compulsory.