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.

       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.
              This can be helpful for media files which often cannot be compressed much more.

       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

                                            2024-11-26                        BORG-COMPRESSION(1)