borg analyze

borg [common options] analyze [options]

options
	--by-name	decompose the whole repository by archive name (not combinable with archive filters)
	--json	format output as JSON
Common options
Archive filters — Archive filters can be applied to repository targets.
	-a PATTERN, --match-archives PATTERN	only consider archives matching all patterns. See “borg help match-archives”.
	--sort-by KEYS	Comma-separated list of sorting keys; valid keys are: timestamp, archive, name, id, tags, host, user; default is: timestamp
	--first N	consider the first N archives after other filters are applied
	--last N	consider the last N archives after other filters are applied
	--oldest TIMESPAN	consider archives between the oldest archive’s timestamp and (oldest + TIMESPAN), e.g., 7d or 12m.
	--newest TIMESPAN	consider archives between the newest archive’s timestamp and (newest - TIMESPAN), e.g., 7d or 12m.
	--older TIMESPAN	consider archives older than (now - TIMESPAN), e.g., 7d or 12m.
	--newer TIMESPAN	consider archives newer than (now - TIMESPAN), e.g., 7d or 12m.

Description

Analyze the archives matching the usual archive selection options (e.g. -a series_name).

Deduplicated size of a set of archives

For the considered (matching) set of archives, borg analyze reports the source (uncompressed source data) and stored (compressed, as stored in the repository) size, plus the compression factor relating the two (stored / source):

• the deduplicated size of the set: the summed size of the union of chunks the considered archives reference (chunks shared within the set are counted once);

• the exclusive size of the set: the summed size of chunks referenced only by the considered set and by no other archive - i.e. the space that deleting the whole set would free (assuming the other archives stay).

Additionally, the unreferenced chunks are reported: chunks in the repository that no non-deleted archive references, i.e. what borg compact could free in the current state of the repository. Only their stored size is known - a chunk’s source size is only recorded in the archives that reference it. Note that chunks belonging to soft-deleted archives count as unreferenced here, although borg compact keeps them when the repository is damaged (so borg undelete stays possible).

If no archive filter is given, all archives are considered - every referenced chunk is then trivially exclusive to them, so only the repository-wide deduplicated size is shown.

The stored sizes come from the repository’s chunk index; the chunk membership and the source sizes come from the per-archive references cache that borg compact maintains, so unchanged archives usually do not need to be opened.

Decomposition by archive name (--by-name)

With --by-name, the whole repository is decomposed by archive name instead. Archives sharing a name form a series, so a name usually groups all backups of one source; for old-style archives that do not form a series, each name is just one archive.

Every chunk is counted in exactly one row, so the rows add up to the repository’s deduplicated size:

• one row per archive name, showing what is exclusive to it: no archive of another name references these chunks, so deleting all archives of that name would free them;

• one row for the chunks shared by two or more names;

• one row for the unreferenced chunks (see above).

This answers “which name costs how much, and what would I get back by dropping it” for all names at once, in a single pass over the archives. As the shared and unreferenced rows can only be determined by looking at every archive, --by-name always covers the whole repository and cannot be combined with archive filters.

Hot spots

If at least two archives match, borg analyze additionally iterates over all matching archives, over all contained files, and collects information about chunks stored in all directories it encounters. It considers chunk IDs and their plaintext sizes and adds up the sizes of added and removed chunks per direct parent directory, and outputs a list of “directory: size”.

You can use that list to find directories with a lot of “activity” — maybe some of these are temporary or cache directories you forgot to exclude. To avoid including these unwanted directories in your backups, you can carefully exclude them in borg create (for future backups) or use borg recreate to recreate existing archives without them.

JSON output

With --json, the same numbers are emitted as a single JSON object instead of the text report, with raw byte values rather than formatted sizes. The default mode fills the dedup_size and hotspots keys, --by-name fills the by_name key. The compression factor is not included: it is stored_size / source_size.

See All about JSON: How to develop frontends for the object’s structure.