NAME

       borg-compression - Details regarding compression

DESCRIPTION

       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 explicitly  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 explicitly 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 explicitly 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.

       obfuscate,SPEC,C[,L]
              Use  compressed-size  obfuscation  to  make  fingerprinting attacks based on the observable stored
              chunk size more difficult. Note:

              • You must combine this with encryption, or it won't make any sense.

              • Your repo size will be bigger, of course.

              • A chunk is limited by the constant MAX_DATA_SIZE (cur. ~20MiB).

              The SPEC value determines how the size obfuscation works:

              Relative random reciprocal size variation (multiplicative)

              Size will increase by a factor, relative to the compressed data size.  Smaller  factors  are  used
              often, larger factors rarely.

              Available factors:

                 1:     0.01 ..        100
                 2:     0.1  ..      1,000
                 3:     1    ..     10,000
                 4:    10    ..    100,000
                 5:   100    ..  1,000,000
                 6: 1,000    .. 10,000,000

              Example probabilities for SPEC 1:

                 90   %  0.01 ..   0.1
                  9   %  0.1  ..   1
                  0.9 %  1    ..  10
                  0.09% 10    .. 100

              Randomly sized padding up to the given size (additive)

                 110: 1kiB (2 ^ (SPEC - 100))
                 ...
                 120: 1MiB
                 ...
                 123: 8MiB (max.)

       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 ...
          borg create --compression obfuscate,110,none ...
          borg create --compression obfuscate,3,auto,zstd,10 ...
          borg create --compression obfuscate,2,zstd,6 ...

AUTHOR

       The Borg Collective

                                                   2024-07-02                                BORG-COMPRESSION(1)