Bastrama is a command-line tool to manage backup files.

Bastrama - Backup Strategy Manager

Bastrama is a command-line tool to manage backup files that are stored on random access memory (eg. hard drives). It implements an infinite grandfather-father-son strategy by deleting a defined subset of the backup files, therefore saving storage space while still keeping some of the older backups in case something went wrong (and needs to be restored from) a long time ago.

The idea is: Bastrama lets you run full daily backups to hard drive and you will just never run out of space. - Of course you'll have to do the backups yourself (using the backup tool of your choice). Bastrama is just managing the resulting backup files.

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• POD Documentation of Bastrama
• Download Bastrama 0.15
• Bastrama project page on SourceForge

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Backup Strategies.

From you backup files, numbered linear starting from 0, Bastrama builds a "tree", where every node has n children. Then from every level of the tree, Bastrama keeps the latest k files. The rest is deleted.
Here are some charts to make it clear. A sequence of backups is drawn from left to right, numbered from 0 to 68, where 0 denotes the oldest backup and 68 the latest (eg. "today's"). Green files are kept, gray ones are deleted.
n=2, k=2

n=2, k=4

n=3, k=3

n=3, k=6

It can be seen that the oldest and the latest backup are always kept. Between them, the probability of a backup being kept decreases exponentially with its age.
As a consequence, the required storage space increases only logarithmically over time, which is very, very slow. (This is assuming, that the later backup files aren't larger than the older ones.).

An example: After 10000 backup cycles with a n=3, k=3 strategy, 18 files are kept:

file kept	age
# 10000	0 cycles
# 9999	1 cycles
# 9998	2 cycles
# 9996	4 cycles
# 9993	7 cycles
# 9990	10 cycles
# 9981	19 cycles
# 9963	37 cycles
# 9936	64 cycles
# 9882	118 cycles
# 9801	199 cycles
# 9720	280 cycles
# 9477	523 cycles
# 8748	1252 cycles
# 8019	1981 cycles
# 6561	3439 cycles
# 4374	5626 cycles
# 0	10000 cycles

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