Due to the fiasco of running rm -rf on my home partition, and wiping out all my backup snapshots, I realised that it is important to have some sort of offline backups. Snapper ¹⁾ creates snapshots, but manual operations are required to move those snapshots off to external backup devices (in order to offline backups). A better solution is desperately needed. I discovered Btrbk ²⁾.

It is much harder to understand, please read the man page. I am just going to document what I did to my own machine.

I created an empty Btrfs partition with a subvolum name home and a directory named snapshots. I mount the partition itself under /mnt/home. I mount the home subvolume under /home.

This is a snippet of my fstab:

# <file system> <mount point>   <type>  <options>       <dump>  <pass>
#Entry for /dev/mapper/illustrious-home:
UUID="a15feee3-8096-409e-ac20-10ae347754c3"    /home        btrfs    ssd,discard,autodefrag,space_cache,subvol=home    0    2

#Entry for /dev/mapper/illustrious-home:
UUID="a15feee3-8096-409e-ac20-10ae347754c3"    /mnt/home    btrfs    ssd,discard,autodefrag,space_cache                0    2

Here is the top level directory layout of the partition that contains my home directory subvolume:

fangfufu@smithsonian:~$ ls /mnt/home
home  snapshots

Here is my Btrbk configuration:

transaction_log            /var/log/btrbk.log
timestamp_format           long-iso
lockfile                   /var/lock/btrbk.lock

volume /mnt/home
        snapshot_preserve       24h 7d 4w
        snapshot_preserve_min   1d
        snapshot_dir snapshots
        subvolume home

volume /mnt/home
        snapshot_preserve       no
        snapshot_preserve_min   latest
        target_preserve         no
        target_preserve         6m
        snapshot_dir offline_snapshots
        snapshot_create ondemand
        subvolume home
        target send-receive /media/fangfufu/Hitachi500GB/home-backups

Basically, my laptop is configured to save 24 hourly snapshots, 7 daily snapshots, 4 weekly snapshots. The external backup drive has 6 months of snapshots. Note that you need two entries for the same subvolume to enable on-demand creation of the offline snapshots. Otherwise the Btrbk throws warnings in Cron.

Btrbk needs to be run hourly, for the whole snapshot thing to work. In order to do that we create /etc/cron.hourly/btrbk with the following content:

#!/bin/sh
exec /usr/sbin/btrbk -q run

Do remember to run chmod +x /etc/cron.hourly/btrbk, so it can be executed.

Btrbk will attempt to send the Btrfs diffs to the external hard drive, if it is attached. If not, then only the snapshot will be created.

All you have to do is type in btrbk run as root. Example output:

root@smithsonian:~# btrbk run
--------------------------------------------------------------------------------
Backup Summary (btrbk command line client, version 0.25.0)

    Date:   Wed Jul  5 22:08:18 2017
    Config: /etc/btrbk/btrbk.conf

Legend:
    ===  up-to-date subvolume (source snapshot)
    +++  created subvolume (source snapshot)
    ---  deleted subvolume
    ***  received subvolume (non-incremental)
    >>>  received subvolume (incremental)
--------------------------------------------------------------------------------
/mnt/home/home
+++ /mnt/home/snapshots/home.20170705T220818+0100
*** /media/fangfufu/Hitachi500GB/home.20170705T220818+0100

Snapshots are accessible under /mnt/home/snapsots.