Btrfs backup scripts

These scripts are a thin wrapper around btrfs for the sake of easily creating, copying and cleaning up backups.

Setup

Create a btrfs filesystem in the block device of your choice:

mkfs.btrfs -L main /dev/sda3

You can use this filesystem as a source of snapshots, or any subvolume thereof.

A typical setup is to create separate subvolumes for the directories you wish to backup independently (say, the root and home directories):

mkdir /mnt/main
mount /dev/sda3 /mnt/main
btrfs subvolume create /mnt/main/root
btrfs subvolume create /mnt/main/home

Create then a backup subvolume that will contain snapshot pools:

btrfs subvolume create /mnt/main/backup

and proceed to create the respective pools for your subvolumes of interest:

btrfs subvolume create /mnt/main/backup/root
btrfs subvolume create /mnt/main/backup/home

In fstab you can specify the mount points of each subvolume:

LABEL=main    /            btrfs    subvol=root                    0 0
LABEL=main    /home        btrfs    subvol=home                    0 0
LABEL=main    /var/backup  btrfs    subvol=backup,noauto,compress  0 0

The advantage of this setup is that mounting / and /home does not result in the backups (i.e. /var/backup) being mounted as well. Indexing tools will not traverse the backups unnecessarily.

The /var/backup pool acts as a local time machine to which you can resort when needed.

Usage

Store a read-only snapshot of a subvolume into a pool:

btrfs-backup-snapshot /home /var/backup/home

Entire pools can be sent to other pools:

btrfs-backup-send /var/backup/home /mnt/external/backup/home

In this way you can copy your local snapshots to external storage.

Pools can be cleaned up to remove old snapshots:

btrfs-backup-clean /var/backup/home
btrfs-backup-clean /mnt/external/backup/home

The cleanup policy (i.e., what an "old" snapshot is) is expressed in terms of filters defined in the cleanup.d directory.

The following is an all-in-one command that is equivalent to all commands shown previously:

btrfs-backup /home /var/backup/home /mnt/external/backup/home

It will take a snapshot of /home, store it in the pool /var/backup/home, send this pool to another pool /mnt/external/backup/home, and cleanup both pools.

Running prediodically

Usually the commands described previously will be invoked on a regular basis from a cron job or systemd timer, for instance to create a snapshot every hour, cleanup the pools once a day, and send your local pools to external storage every 3 hours.

The config branch of this repository contains examples of scripts you can invoke as a periodic job. These can be symlinked to your /usr/local/bin.

Possible improvements

• Have pool-specific cleanup policies, when a .btrfs-backup-cleanup.d subdirectory is found inside a snapshot pool. The current global 'cleanup.d` directory would serve as default policy.

Acknowledgements

https://btrfs.wiki.kernel.org/index.php/Incremental_Backup