Bi·lak

When I started playing with LXD I just accepted the default storage configuration which creates an image file and uses that to initialize a ZFS pool. Since I’m using ZFS as my main file system this seemed silly as LXD can use an existing dataset as a source for a storage pool. So I wanted to migrate my existing containers to the new storage pool.

Although others seemed to to have the same problem there was no ready answer. Digging through the documentation I finally found out that the lxc move  command had a -s  option … I had an idea. ? Here’s what I came up with …

Preparation

First we create the dataset on the existing ZFS pool and add it to LXC.

sudo zfs create -o mountpoint=none mypool/lxd
lxc storage create pool2 zfs source=mypool/lxd

lxc storage list should show something like this now:

+-------+-------------+--------+--------------------+---------+
| NAME  | DESCRIPTION | DRIVER |       SOURCE       | USED BY |
+-------+-------------+--------+--------------------+---------+
| pool1 |             | zfs    | /path/to/pool1.img | 2       |
+-------+-------------+--------+--------------------+---------+
| pool2 |             | zfs    | mypool/lxd         | 0       |
+-------+-------------+--------+--------------------+---------+

pool1 is the old pool backed by the image file and is used by some containers at the moment as can be seen in the “Used By” column. pool2 is added by not used by any contaiers yet.

Moving

We now try to move our containers to pool2.

# move container to pool2
lxc move some_container some_container-moved -s=pool2
# rename container back for sanity ;)
lxc move some_container-moved some_container

We can check with lxc storage list whether we succeeded.

+-------+-------------+--------+--------------------+---------+
| NAME  | DESCRIPTION | DRIVER |       SOURCE       | USED BY |
+-------+-------------+--------+--------------------+---------+
| pool1 |             | zfs    | /path/to/pool1.img | 1       |
+-------+-------------+--------+--------------------+---------+
| pool2 |             | zfs    | mypool/lxd         | 1       |
+-------+-------------+--------+--------------------+---------+

Indeed pool2 is beeing used now. ? Just to be sure we check that zfs list -r mypool/lxd  also reflects this.

NAME                                  USED  AVAIL  REFER  MOUNTPOINT
mypool/lxd/containers                 1,08G  92,9G    24K  none
mypool/lxd/containers/some_container  1,08G  92,9G   704M  /var/snap/lxd/common/lxd/storage-pools/pool2/containers/some_container
mypool/lxd/custom                       24K  92,9G    24K  none
mypool/lxd/deleted                      24K  92,9G    24K  none
mypool/lxd/images                       24K  92,9G    24K  none
mypool/lxd/snapshots                    24K  92,9G    24K  none

Awesome!

⚠ Note that this only moves the container, but not the LXC image it was cloned off of.

We can repeat this until all containers we care about are moved over to pool2.

Cleanup

To prevent new containers to use pool1  we have to edit the default  profile.

# change devices.root.pool to pool2
lxc profile edit default

Finally …. when we’re happy with the migration and we’ve verified that everything works as expected we can now remove pool1.

lxc storage rm pool1