Btrfs snapshots allow you to create efficient backups of your filesystem.

We’ll explore some of the basics of Btrfs snapshots and their practical applications.

Snapshot feature of Btrfs uses the Copy-on-Write (CoW) strategy. So it doesn’t take much disk space and snapshots of subvolumes are instantaneous.

Two snapshot types:

• read-write: the snapshot file and directories may be modified. This is the default type.
• read-only: the snapshot files and directories can not be modified.

Friendly subvolumes layout

It may be a good idea to heave separated subvolumes for /home and /.snapshots folders.

Mount the btrfs root subvolume:

    $ mount -t btrfs -o subvolid=5 /dev/sda2 /mnt/btrfs

Create the required subvolumes at the same level of the root subvolume:

    $ sudo btrfs subvolume create /mnt/btrfs/@home
    $ sudo btrfs subvolume create /mnt/btrfs/@snapshots

This is the layout we’re going to get

    subvolid=5
      +--- @rootfs
      +--- @home
      +--- @snapshots

Modify the fstab file in order to automatically mount the subvolumes.

    UUID=<disk-uid>   /           btrfs  defaults,subvol=@rootfs    0  0
    UUID=<disk-uid>   /home       btrfs  defaults,subvol=@home      0  0
    UUID=<disk-uid>   /.snapshots btrfs  defaults,subvol=@snapshots 0  0

Mount the @home subvolume to a temporary folder and move the content of your /home directory into it. Reboot

Snapshots

Take a read-only snapshot of the home filesystem.

    $ btrfs subvolume snapshot -r /home /.snapshots/home-snap

Snapshots will not take recursive snapshots of themselves. If you create a snapshot of a subvolume, every subvolume or snapshot that the subvolume contains is mapped to an empty directory of the same name inside the snapshot.

To view snapshot subvolume details:

    $ btrfs subvolume show /.shapshots/home-snap

Recovery

To restore an old snapshot is sufficient to manually restore it.

There are different solutions, for example we can use mv, rsync or btrfs tool.

Mount the destination subvolume to a temporary folder:

    $ mount -t btrfs -o subvolid=<ID> /dev/<device> /mnt

Align to the snapshot:

    $ rsync -arv --progress --delete /.snapshots/<snap> /mnt/

It is important to exclude the snapshots folder from the synch procedure.

Send and Receive

Is possible to transfer a snapshot to another btrfs volume (e.g. on an external hard drive).

    $ btrfs send /.snapshots/snap1 | btrfs receive /mnt/data/dest

This is called initial bootstrapping, and it corresponds to a full backup. This task will take some time, depending on the size of the snapshot directory.

Subsequent incremental sends will take a shorter time.

Incremental

Take another snapshot.

    $ btrfs subvolume snapshot -r /home /.snapshots/snap2

Send only the differences

    $ btrfs send -p /.snapshots/snap1 /.snapshots/snap2 | \
      btrfs receive /mnt/data/dest

Snapper

Snapper is a tool that helps manage snapshots of btrfs subvolumes.

It can create and compare snapshots, revert between snapshots, and support automatic snapshots’ timelines.

Configuration

Before creating a configuration for a subvolume, the subvolume must already exist.

To create a new configuration named myconfig for the btrfs subvolume at /path/to/subvol, run:

    $ snapper -c myconfig create-config /path/to/subvol

The command creates:

• a configuration file at /etc/snapper/configs/myconfig using the default template and creates a subvolume at
• a subvolume at /path/to/subvol/.snapshots where future snapshots for this configuration will be stored.

For example

    $ snapper -c root create-config /

Custom snapshot subvolume

During configuration snapper creates a subvolume to store all the snapshots as a child of the @rootfs subvolume.

    subvolid=5 (btrfs root)
      +--- @rootfs
              +--- .snapshots

To simplify revert operations we prefer to use the @snapshots subvolume created as a child of btrfs root (subvolid=5)

Remove the volume created by snapper:

sudo btrfs subvolume delete /.snapshots

Mount our @snapshots subvolume in the /.snapshots folder

sudo mount -o subvol=@snapshots /dev/<device> /.snapshots

Restore snapshot

Restoring a snapshot involves copying things around from an old snapshot to the current state.

To simplify the process we are going to use snapper-rollback, a simple python script to rollback systems using Arch wiki suggested subvolume layout.

A Debian package for script can be found here.

Once installed the configuration in /etc/snapper-rollback.conf should be adjusted to reflect your system and snapper configuration. Mine:

[root]
subvol_main = @rootfs
subvol_snapshots = @snapshots
mountpoint = /mnt/btrfs
dev = /dev/nvme0n1p2

Debian apt hook

Debian installation comes with the /etc/apt/apt.conf.d/80snapper hook for apt.

This hook invokes snapper before and after apt modifications to create a pre and post subvolume snapshot.

The hook will use the configuration referenced by /etc/default/snapper.