Increasing the default ZFS Loop Device value in LXD on Ubuntu

I’ve recently installed LXD 2.x on my Ubuntu server but forgot to set a custom value for the loop device. The default value was 20GB, but I wanted this to be 1.4TB.

It took a while of searching accross the web to find an easy solution to increase this size, as I found it tricky I have posted the solution I have used below, with some help from these posts: here and here.

These commands were tested with LXD version 2.0.11 running on Ubuntu 16.04.5 LTS 64-Bit, read the docs for your current LXD and ZFS versions before you run any of these, and make sure you have a backup incase anything goes wrong!

Change these values to match your setup:

  • POOL-NAMEYour ZFS pool name, the default supplied by LXD is ‘lxd’
  • SIZEThe size of the new pool, e.g. ’50G’

Now run this code; each line separately minus the commented lines:

# Ensure 'autoexpand' is enabled (only needed once)
sudo zpool set autoexpand=on POOL-NAME

# Create a new XXGB file, and replace the current version
sudo truncate -s SIZE /var/lib/lxd/zfs.tmp
sudo zpool attach POOL-NAME /var/lib/lxd/zfs.img /var/lib/lxd/zfs.tmp
sudo zpool detach POOL-NAME /var/lib/lxd/zfs.img
sudo rm /var/lib/lxd/zfs.img

sudo truncate -s SIZE /var/lib/lxd/zfs.img
sudo zpool attach POOL-NAME /var/lib/lxd/zfs.tmp /var/lib/lxd/zfs.img
sudo zpool detach POOL-NAME /var/lib/lxd/zfs.tmp
sudo rm /var/lib/lxd/zfs.tmp

# Force ZFS to pickup the new changes, use the new partition which is the same
sudo zpool online -e POOL-NAME /var/lib/lxd/zfs.img /var/lib/lxd/zfs.img

You can also, check if the settings have been applied by running the sudo zfs list command, you will see a result similar to below; make note of the values in the ‘AVAIL’ column as this should show your new pool size.

root@ubuntu-s-6vcpu-16gb-lon1-01:/# sudo zfs list
NAME                                                                          USED  AVAIL  REFER  MOUNTPOINT
lxd                                                                           646M   125G    19K  none
lxd/containers                                                               12.7M   125G    19K  none
lxd/containers/container1                                                    6.28M   125G   307M  /var/lib/lxd/containers/container1.zfs
lxd/containers/container2                                                    6.38M   125G   326M  /var/lib/lxd/containers/container2.zfs
lxd/images                                                                    633M   125G    19K  none
lxd/images/2d53824fdf89b011d6b3178dc2d70bc7932ad93d81b42aa2eae5ac78c5d59e3a   326M   125G   326M  /var/lib/lxd/images/2d53824fdf89b011d6b3178dc2d70bc7932ad93d81b42aa2eae5ac78c5d59e3a.zfs
lxd/images/9023b2feede581884cf45be29f60207ccc5553d762ea8088e849858a58762f6b   307M   125G   307M  /var/lib/lxd/images/9023b2feede581884cf45be29f60207ccc5553d762ea8088e849858a58762f6b.zfs
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