rmexpbak
Delete backups leaving only a very small fraction of them.
Before I upgrade my system I make a backup of the root filesystem in the form of
a Btrfs snapshot in /media/hdd/backups. These backups end up taking a lot of
space, so I regularly delete some of them. However, it can be tricky to decide
which backups to delete.
Suppose in /media/hdd/backups I have 5 btrfs snapshots named by date.
2021-09-25 2021-11-07 2021-12-01 2022-01-15 2022-02-27
This program groups backups into increasing powers of two and deletes all but one backup in the group. This means an exponential number of backups are deleted and a logarithmic amount of backups are kept. Since so few backups are kept a lot of disk space is saved.
2021-09-25 2021-11-07 | 2021-12-01 2022-01-15 | 2022-02-27 |
Group of 4 backups | Group of 2 backups | Group of 1 backup |
Keep one backup in each group.
| 2022-01-15 | 2022-02-27 |
Group of 4 backups | Group of 2 backups | Group of 1 backup |
Note the "Group of 4 backups" deletes all the backups because there is not enough backups to make a real group of 4.
Of the 5 backups in the example above, only floor(lb(5)) = 2 are kept. The pruning is more drastic if there are more backups. For example, if there were 256 backups, only 8 would be kept. This allows you to make backups everyday without wasting a lot of space.
The will program remember the backups it deleted, so running the program twice on the same directory should be a no-op if no additional backups have been made.
Usage
For the program to work, it needs to know the command used to delete backups.
Create a Dhall configuration file named
.rmexpbak.dhall in the directory containing the backups. e.g.
{rmCmd = ["btrfs", "subvolume", "delete"]}Run rmexpbak <path to backups> to see the commands the program will run. Once
you are satisfied, run rmexpbak --delete <path to backups> to actually delete
the backups. e.g.
$ tee /media/hdd/backups/.rmexpbak.dhall << EOF
{rmCmd = ["btrfs", "subvolume", "delete"]}
EOF
$ rmexpbak /media/hdd/backups/
Dry-run. Specify --delete to actually delete files
["btrfs","subvolume","delete","/media/hdd/backups/2021-09-25"]
["btrfs","subvolume","delete","/media/hdd/backups/2021-11-07"]
["btrfs","subvolume","delete","/media/hdd/backups/2021-12-01"]
Dry-run. Specify --delete to actually delete files
$ rmexpbak --delete /media/hdd/backups
["btrfs","subvolume","delete","/media/hdd/backups/2021-09-25"]
Delete subvolume (no-commit): '/media/hdd/backups/2021-09-25'
["btrfs","subvolume","delete","/media/hdd/backups/2021-11-07"]
Delete subvolume (no-commit): '/media/hdd/backups/2021-11-07'
["btrfs","subvolume","delete","/media/hdd/backups/2021-12-01"]
Delete subvolume (no-commit): '/media/hdd/backups/2021-12-01'Pre-commit checklist
- Run tests (
stack test) - Run coverage on unit tests (
stack test --coverage) - Run hlint (
hlint .)