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docs: Small changes regarding compression

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- Mention zstd as the best general choice when not using lz4
  (as often acknowledged by public benchmarks)
- Mention 'auto' more prominently as a good heuristic to improve
  speed while retaining good compression
- Link to compression options
This commit is contained in:
Martin Richtarsky 2024-10-22 08:26:14 +02:00
parent 411f6f3222
commit f656f6b1f2
2 changed files with 16 additions and 21 deletions
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34
docs/quickstart.rst
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@ -292,35 +292,29 @@ Backup compression
------------------
The default is lz4 (very fast, but low compression ratio), but other methods are
supported for different situations.
supported for different situations. Compression not only helps you save disk space,
but will especially speed up remote backups since less data needs to be transferred.
You can use zstd for a wide range from high speed (and relatively low
compression) using N=1 to high compression (and lower speed) using N=22.
zstd is a modern compression algorithm and might be preferable over zlib and
lzma.::
zstd is a modern compression algorithm which can be parametrized to anything between
N=1 for highest speed (and relatively low compression) to N=22 for highest compression
(and lower speed)::
$ borg create --compression zstd,N arch ~
Other options are:
If you have a fast repo storage and you want minimum CPU usage, no compression::
If you have a fast repo storage and you want minimum CPU usage you can disable
compression::
$ borg create --compression none arch ~
If you have a less fast repo storage and you want a bit more compression (N=0..9,
0 means no compression, 9 means high compression):
You can also use zlib and lzma instead of zstd, although zstd usually provides the
the best compression for a given resource consumption. Please see :ref:`borg_compression`
for all options.
::
An interesting alternative is ``auto``, which first checks with lz4 whether a chunk is
compressible (that check is very fast), and only if it is, compresses it with the
specified algorithm::
$ borg create --compression zlib,N arch ~
If you have a very slow repo storage and you want high compression (N=0..9, 0 means
low compression, 9 means high compression):
::
$ borg create --compression lzma,N arch ~
$ borg create --compression auto,zstd,7 arch ~
You'll need to experiment a bit to find the best compression for your use case.
Keep an eye on CPU load and throughput.

3
src/borg/archiver/help_cmd.py
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@ -417,7 +417,8 @@ class HelpMixIn:
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.
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