borg/docs/man/borg-compression.1

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.TH BORG-COMPRESSION 1 "2017-05-17" "" "borg backup tool"
.SH NAME
borg-compression \- Details regarding compression
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.SH DESCRIPTION
.sp
Compression is lz4 by default. If you want something else, you have to specify what you want.
.sp
Valid compression specifiers are:
.sp
none
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Do not compress.
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.sp
lz4
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Use lz4 compression. High speed, low compression. (default)
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.sp
zlib[,L]
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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.
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.sp
lzma[,L]
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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.
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.sp
auto,C[,L]
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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.
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.sp
Examples:
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.sp
.nf
.ft C
borg create \-\-compression lz4 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 ...
.ft P
.fi
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.sp
General remarks:
.sp
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).
.sp
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.
.SH AUTHOR
The Borg Collective
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