Introduction

This HOWTO covers how to converting a qcow2 disk image to a ZFS volume.

This process can be useful if you are migrating virtual machine storage or take advantage of the snapshot functionality in the ZFS filesystem.

Prerequisites

A working ZFS installation with free space
The qemu-img command line utility
The qemu-nbd command line utility
Kernel support for nbd

doas modprobe nbd

Steps

The following steps needs to be performed

Verify the qcow2 Image

qemu-img check /path/to/image.qcow2

Connect the qcow2 Image to a Network Block Device

doas qemu-nbd --connect=/dev/nbd0 /path/to/image.qcow2

Get the size of the current virtual disk

doas blockdev --getsize64 /dev/nbd0

Create the ZFS Volume

doas zfs create -V <REPLACE_THIS_WITH_THE_OUTPUT_OF_THE_PREVIOUS_COMMAND>b <ENTER_THE_ZFS_PATH>

# Example:
# doas zfs create -V zfs create -V 4294967296b  zpool/ROOT/vm/vm1-vda

Copy the disk

doas dd if=/dev/nbd0 of=/dev/zvol/<PATH_TO_YOUR_CREATED_ZFS_VOLUME> bs=4096 status=progress

# Example:
# doas dd if=/dev/nbd0 of=/dev/zvol/zpool/ROOT/vm/vm1-vda bs=4096 status=progress

Disconnect the qcow2 image

doas qemu-nbd --disconnect /dev/nbd0

Update your Configuration

Update the configuration that previously used the .qcow2 image to instead use the block device proviced by ZFS (/dev/zvol/)

Migrate Qcow2 to ZFS volume