Customize pruning

To understand the custom options, we first explain how the pruning process works:

1. All snapshots and directories within snapshots are scanned to determine which data is still in use.

2. For all files in the repository, rustic finds out if the file is fully used, partly used or completely unused.

3. Completely unused files are marked for deletion. Fully used files are kept. A partially used file is either kept or marked for repacking depending on user options.

   Note that for repacking, rustic must download the file from the repository storage and re-upload the needed data in the repository. This can be very time-consuming for remote repositories.

4. After deciding what to do, prune will actually perform the repack, modify the index according to the changes and delete the obsolete files.

The prune command accepts the following options:

• --max-unused limit allow unused data up to the specified limit within the repository. This allows rustic to keep partly used files instead of repacking them.

  The limit can be specified in several ways:

  • As an absolute size (e.g. 200M). If you want to minimize the space used by your repository, pass 0 to this option.
  • As a size relative to the total repo size (e.g. 10%). This means that after prune, at most 10% of the total data stored in the repo may be unused data. If the repo after prune has a size of 500MB, then at most 50MB may be unused.
  • If the string unlimited is passed, there is no limit for partly unused files. This means that as long as some data is still used within a file stored in the repo, rustic will just leave it there. Use this if you want to minimize the time and bandwidth used by the prune operation. Note that metadata will still be repacked.

  rustic tries to repack as little data as possible while still ensuring this limit for unused data. The default value is 5%.

• --max-repack-size size if set limits the total size of files to repack. As prune first stores all repacked files and deletes the obsolete files at the end, this option might be handy if you expect many files to be repacked and fear to run low on storage.

• --repack-cacheable-only if set to true only files which contain metadata and would be stored in the cache are repacked. Other pack files are not repacked if this option is set. This allows a very fast repacking using only cached data. It can, however, imply that the unused data in your repository exceeds the value given by --max-unused. The default value is false.

• --dry-run only show what prune would do.

• --verbose increased verbosity shows additional statistics for prune.