borg-compression - Details regarding compression
It is no problem to mix different compression methods in one repo,
deduplication is done on the source data chunks (not on the compressed or
encrypted data).
If some specific chunk was once compressed and stored into the
repo, creating another backup that also uses this chunk will not change the
stored chunk. So if you use different compression specs for the backups,
whichever stores a chunk first determines its compression. See also borg
recreate.
Compression is lz4 by default. If you want something else, you
have to specify what you want.
Valid compression specifiers are:
- none
- Do not compress.
- lz4
- Use lz4 compression. Very high speed, very low compression. (default)
- zstd[,L]
- Use zstd ("zstandard") compression, a modern wide-range
algorithm. If you do not explicitely give the compression level L (ranging
from 1 to 22), it will use level 3. Archives compressed with zstd are not
compatible with borg < 1.1.4.
- zlib[,L]
- Use zlib ("gz") compression. Medium speed, medium compression.
If you do not explicitely give the compression level L (ranging from 0 to
9), it will use level 6. Giving level 0 (means "no compression",
but still has zlib protocol overhead) is usually pointless, you better use
"none" compression.
- lzma[,L]
- Use lzma ("xz") compression. Low speed, high compression. If you
do not explicitely give the compression level L (ranging from 0 to 9), it
will use level 6. Giving levels above 6 is pointless and counterproductive
because it does not compress better due to the buffer size used by borg -
but it wastes lots of CPU cycles and RAM.
- auto,C[,L]
- Use a built-in heuristic to decide per chunk whether to compress or not.
The heuristic tries with lz4 whether the data is compressible. For
incompressible data, it will not use compression (uses "none").
For compressible data, it uses the given C[,L] compression - with C[,L]
being any valid compression specifier.
Examples:
borg create --compression lz4 REPO::ARCHIVE data
borg create --compression zstd REPO::ARCHIVE data
borg create --compression zstd,10 REPO::ARCHIVE data
borg create --compression zlib REPO::ARCHIVE data
borg create --compression zlib,1 REPO::ARCHIVE data
borg create --compression auto,lzma,6 REPO::ARCHIVE data
borg create --compression auto,lzma ...