Tag: Data Storage

Century-Scale Storage

What would you use to keep (digital) data safe for at least a hundred years? Maxwell Neely-Cohen looks at all the factors, possible technologies, social and economic challenges that you have to contend with if you intentionally want to store data for a century. He explicitly chose that time scale, because it is at the edge of what a human can experience, but it is outside of a single human’s work life as well as beyond the lifetime of most companies or institutions. So the premise sets you up for a host of problems to be solved. He also analyses strategies for recording and keeping data past and present and evaluates their potential for keeping data safe at century-scale.
It’s long, but worth it.

Moving LXD Containers From One Pool to Another

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