btrfs snapshot and backup tools

Disclaimer: I wrote these tools for my own personal use. They may be insecure and full of horrible bugs. That said, they work fine for me.

The scripts btrsnap and btrsend make some assumptions about your filesystem layout. See btrsnap for details. These scripts are provided mostly as working examples for someone trying to use btrsend.rkt. You may wish to manage your snapshots differently; btrsend.rkt does not really care how you manage your snapshots.

In my setup, btrsnap is invoked nightly from root's crontab.

WARNING: The manner in which btrsend calls a user's ~/.btrsend is probably insecure.

btrsend.rkt

This is the interesting part. This script manages the storage of complete and incremental backups on Amazon Glacier ( http://aws.amazon.com/glacier/ ). When it is invoked with the date for which a backup is to be made, it will either output nothing, the ASCII string c followed by a newline, or an ASCII string of the form i YYYY-MM-DD followed by a newline, where YYYY, MM, and DD form a date.

When nothing is output, this indicates that no backup is to be made for this date according to the schedule. The program exits immediately.

When c is output, a complete serialization of the snapshot for the provided date is expected on stdin.

When i YYYY-MM-DD is output, an incremental serialization of the snapshot from YYYY-MM-DD to the snapshot for the provided date is expected.

Take care to map dates to snapshots in a consistent way. If, for example, you were to tell btrsend.rkt that it was backing up for the date 1992-01-01 and then later resolve 1992-01-01 to a snapshot other than the one provided on stdin, it may be impossible to restore the Glacier archives uploaded by btrsend.rkt.

btrsend.rkt compresses its input with gzip -7 and encrypts asymmetrically (not really, symmetric + asymmetrically encrypted key) with gpg. To tune this behaviour, search the source for make-gpg-comress-pipe.

Each complete or incremental blob is compressed, encrypted, and uploaded to Amazon Glacier as a single archive in a streaming manner. Old archives are eventually deleted. All activity is logged to .btrsend.log. An sqlite3 database of active backup archives including lineage and size is maintained in .btrsend.db. The backup schedule is set up as follows:

• A backup is created on the 1st, 7th, 14, and 21st of every month.
• A complete backup is created after a chain of 11 incremental backups have been created from the most recent complete backup or when no complete backup already exists.
• When the most recent backup in a chain of incremental backups is more than 90 days old, the entire chain is deleted.

This schedule may be adjusted by editing the constants at the top of the backup-planner function. Changing them will probably break the built-in test suite.

To run tests, raco test btrsend.rkt

To use btrsend.rkt with the scripts described above:

• Create something executable called ~/.btrsend . Make it chdir to your home directory and then exec btrsend.rkt with its own argv.
• Set up the scripts and required directory structure somewhere.
• Add an entry to root's crontab such that btrsnap is executed every midnight.

To get btrsend.rkt to read your AWS credentials see https://github.com/greghendershott/aws .

WARNING

Backups are very cheap to create and store. Backups can be very expensive to restore. Read the Glacier pricing guide before attempting to restore. Retrieve files slowly to avoid getting an absurdly high bill.