Can I create mirror of 2disk zfs pool with a third disk?

[wagner]

I have Googled a lot today, but cannot find what I am looking for.

I am using the zfs module under Ubuntu.
Here is a link to the reference I used to setup zfs under Ubuntu 11.10
https://github.com/dajhorn/pkg-zfs/wiki/HOWTO-install-Ubuntu-to-a-Native-ZFS-Root-Filesystem

I have created a zfs pool with to 400GB drives (800GB pool)
I have a USB drive 1.5TB that I would like to mirror an 800GB
partition
with the 800GB zfs pool created from the two 400GB drives.

I cannot figure out a way to do that. Here is a sampling of the
errors I get, depending on how I have tried to do it:

# using the zfs 800GB label: zfs_800
wagner@dreamweaver:~$ sudo zpool attach zfs_800 zfs_800 /dev/disk/by-
id/wwn-0x5000c5003d862596-part2
cannot attach /dev/disk/by-id/wwn-0x5000c5003d862596-part2 to zfs_800:
no such device in pool

#using the "id" for the zfs 800GB pool: 18299948817295271399
#I obtained that id from running: sudo zpool export zfs_800, then
sudo zpool import
wagner@dreamweaver:~$ sudo zpool attach zfs_800 18299948817295271399 /
dev/disk/by-id/wwn-0x5000c5003d862596-part2
cannot attach /dev/disk/by-id/wwn-0x5000c5003d862596-part2 to
18299948817295271399: can only attach to mirrors and top-level disks

# A final attempt that also fails
wagner@dreamweaver:~$ sudo zpool create zfs_800_mirror /dev/disk/by-id/
wwn-0x5000c5003d862596-part2 18299948817295271399
cannot open '18299948817295271399': no such device in /dev

I have not found anything on the internet that definitively says
that I can or can't do this. I have found numerous examples
mirroring zfs raid pools, etc., but not my situation, which is to
simply
mirror a single large drive partition with a zfs striped pool from two
smaller disks of the same size as the large disk's partition.

I am interested in this approach as a live backup of the 800GB pool
from the two internal drives with an external USB drive for redundancy
and offline backup when I am not actively working with the data I will
have on this filesystem.

LEW

[Gordan Bobic]

I think you'll find the KQ ZFS port has been discontinued. You may want
to ask the question on the ZoL list instead.

Have a look here:

http://zfsonlinux.org/

The KQ ZFS port was based on an old version of ZoL code.

Gordan