Newbie question on ZFS on FreeBSD

andrew clarke mail at
Sun Apr 27 12:33:09 UTC 2014

On Sat 2014-04-26 06:55:31 UTC+0200, Martin Braun (yellowgoldmine at wrote:

> I am currently running a setup using NFS on Linux with 2x4TB, 1x3TB and 1x1TB.
> Now I want to buy 2x2TB and install FreeBSD with ZFS on for raidz. In
> that setup I want to use the two old 4TB disks so I get a ZFS with
> 4x4TB.
> As I understand in raidz I would then have 12TB of storage and the
> last 4TB is for redundancy.
> However, is it possible to use ZFS on 2x2TB for installation and then
> later add 2x2TB for the raidz, so I end up with a pool of 12TB and 4TB
> for redundancy, or do I need 4x4TB clean disks before I begin?
> In other words.. I want raidz, but I have a lot of data on the two old
> 4TB disks, how do I best deal with the situation?

I run two FreeBSD servers with a fairly boring 2x1TB mirror ZFS
configured on each, so can't really answer you directly, but before I
used ZFS on bare metal I experimented with it using a virtual machine
and learned how to configure it how I wanted. I'd recommend doing that
if possible. In the VM you can use sets of very small (less than 1 GB)
virtual drives - the process is the same for much larger physical

Also, note that you can enlarge a ZFS pool by adding a higher capacity
drive without needing to reformat (nor reboot, for that matter).
That's something you can experiment with in a VM too, obviously.


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