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ZFS - Add a Mirror to an Existing ZFS Drive

Convert the most basic ZFS pool, a system with a single disk, to a Mirror or Stripe.

Current Setup:

We have a single disk attached to our system, /dev/da1
This disk is used as a simple zfs pool, tank
You bought another disk and want to mirror the pool to the new disk, /dev/da2

Ensure the disk names are correct

Make sure you’ve got the disk names correct.

Use dmesg to see the system messages, to determine which disk is which.

ALERT: This can be dangerous if you use the wrong disk, as it will destroy all data on the selected disk.

Delete any existing partitions if needed.

sudo gpart destroy -F /dev/da2

Format the drive as gpt:

sudo gpart create -s gpt /dev/da2

Create a zfs partition:

sudo gpart add -t freebsd-zfs /dev/da2

This new partition is /dev/da2p1, and will nbe added to the existing partition next.