This repository contains shell scripts for creating and managing incremental backups on encrypted BTRFS filesystems.

Author

Georg Sauthoff mail@georg.so

Example

Setup Steps

Create configuration file:

# cat config.sh
DEVICE=/dev/sdb
NAME=backup
TARGET=/mnt/backup
SOURCE=(/home /root /etc /var example.org:/home)

Initialize disk drive:

# bash create.sh -c config.sh

Regular Usage

# bash mount.sh  -c config.sh
# bash backup.sh -c config.sh
# bash umount.sh -c config.sh

Overview

BTRFS is a copy on write file system that supports fast snapshotting. Thus, using it for for incremental backups suggests itself. Basically, the backup involves simply rsyncing locations to a BTRFS mount, creating daily/weekly etc. read-only snapshots (which are normal filesystem locations) and that's it. For encryption, the BTRFS filesystem is created on a luks-encrypted device-mapper device.

Advantages:

• speed - especially when doing incremental backups I've observed for example a speedup of 2 against Dar. In my tests I used rsync in whole-file-copy mode (which is also the default when syncing between local disks), thus, the speedup does not come from a reduced number of tranfered bytes.
• easy retrieval - the restore of the last or any previous snapshots can be done via simple filesystem commands. No need to restore several increments on each other or to construct some kind of catalogue.
• data integrity - since BTRFS checksums all filesystem data, errors are detected. The checksums are verified during normal filesystem operation - but it is also possible to explicitly verify a complete volume (cf. btrfs-scrub(8)).

Backup Schedule

The default backup schedule used by the backup.sh script is:

# days weeks months years
PLAN=${PLAN:-8 3 6 5}

Meaning that snapshots of the last 8 days, the last 3 weaks, the last 6 months and last 5 years are retained.

Note that the creation of a new snapshot is edge-triggered. In other words, the year, the week number etc. are extracted from the current date and are used for creation of the corresponding snapshots, iff a snapshot with the same name does not exist. For example, when running the script every day, the yearly snapshot is created on January the 1st, the weekly on each Monday, the monthly on the 1st of each month and so on.

Directory Layout

The top level directory layout created by the create.sh on a target - say - /mnt/backup is:

/mnt/backup
├── mirror
└── snapshot

When backing up two example hosts the mirror hierarchy could look like:

/mnt/backup/mirror
├── foo.example.org
│   ├── etc
│   ├── home
│   ├── root
│   └── var
└── bar.example.org
    ├── etc
    ├── home
    └── var

Where the snapshot hierarchy might look like:

/mnt/backup/snapshot
├── day
│   ├── 2014-10-10
│   ├── 2014-10-11
│   ├── 2014-10-12
│   ├── 2014-10-13
│   ├── 2014-10-14
│   ├── 2014-10-15
│   ├── 2014-10-23
│   └── 2014-10-24
├── month
│   ├── 2014-07
│   ├── 2014-08
│   ├── 2014-09
│   └── 2014-10
├── week
│   ├── 2014-41
│   ├── 2014-42
│   └── 2014-43
└── year
    └── 2014

Note that there is not a snapshot for each of the last 8 days (assuming that today is October, 24th), but rather for the last 8 days where the backup script was executed.

Under each snapshot directory the state of the mirror directory is frozen (read-only).

All those directory trees can be accessed using standard filesystem operations.

License

GPLv3+