mirror of https://github.com/borgbackup/borg.git
157 lines
4.3 KiB
Groff
157 lines
4.3 KiB
Groff
.\" Man page generated from reStructuredText.
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.TH BORG-COMPRESSION 1 "2017-02-05" "" "borg backup tool"
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.SH NAME
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borg-compression \- Details regarding compression
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..
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.de1 INDENT
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.de UNINDENT
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. RE
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..
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.SH DESCRIPTION
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.sp
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Compression is off by default, if you want some, you have to specify what you want.
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.sp
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Valid compression specifiers are:
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.sp
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none
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.INDENT 0.0
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.INDENT 3.5
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Do not compress. (default)
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.UNINDENT
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.UNINDENT
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.sp
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lz4
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.INDENT 0.0
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.INDENT 3.5
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Use lz4 compression. High speed, low compression.
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.UNINDENT
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.UNINDENT
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.sp
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zlib[,L]
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.INDENT 0.0
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.INDENT 3.5
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Use zlib ("gz") compression. Medium speed, medium compression.
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If you do not explicitely give the compression level L (ranging from 0
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to 9), it will use level 6.
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Giving level 0 (means "no compression", but still has zlib protocol
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overhead) is usually pointless, you better use "none" compression.
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.UNINDENT
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.UNINDENT
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.sp
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lzma[,L]
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.INDENT 0.0
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.INDENT 3.5
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Use lzma ("xz") compression. Low speed, high compression.
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If you do not explicitely give the compression level L (ranging from 0
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to 9), it will use level 6.
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Giving levels above 6 is pointless and counterproductive because it does
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not compress better due to the buffer size used by borg \- but it wastes
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lots of CPU cycles and RAM.
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.UNINDENT
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.UNINDENT
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.sp
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auto,C[,L]
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.INDENT 0.0
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.INDENT 3.5
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Use a built\-in heuristic to decide per chunk whether to compress or not.
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The heuristic tries with lz4 whether the data is compressible.
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For incompressible data, it will not use compression (uses "none").
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For compressible data, it uses the given C[,L] compression \- with C[,L]
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being any valid compression specifier.
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.UNINDENT
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.UNINDENT
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.sp
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The decision about which compression to use is done by borg like this:
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.INDENT 0.0
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.IP 1. 3
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find a compression specifier (per file):
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match the path/filename against all patterns in all \-\-compression\-from
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files (if any). If a pattern matches, use the compression spec given for
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that pattern. If no pattern matches (and also if you do not give any
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\-\-compression\-from option), default to the compression spec given by
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\-\-compression. See docs/misc/compression.conf for an example config.
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.IP 2. 3
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if the found compression spec is not "auto", the decision is taken:
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use the found compression spec.
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.IP 3. 3
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if the found compression spec is "auto", test compressibility of each
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chunk using lz4.
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If it is compressible, use the C,[L] compression spec given within the
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"auto" specifier. If it is not compressible, use no compression.
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.UNINDENT
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.sp
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Examples:
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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borg create \-\-compression lz4 REPO::ARCHIVE data
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borg create \-\-compression zlib REPO::ARCHIVE data
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borg create \-\-compression zlib,1 REPO::ARCHIVE data
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borg create \-\-compression auto,lzma,6 REPO::ARCHIVE data
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borg create \-\-compression\-from compression.conf \-\-compression auto,lzma ...
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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compression.conf has entries like:
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.nf
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.ft C
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# example config file for \-\-compression\-from option
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#
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# Format of non\-comment / non\-empty lines:
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# <compression\-spec>:<path/filename pattern>
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# compression\-spec is same format as for \-\-compression option
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# path/filename pattern is same format as for \-\-exclude option
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none:*.gz
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none:*.zip
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none:*.mp3
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none:*.ogg
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.ft P
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.fi
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.UNINDENT
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.UNINDENT
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.sp
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General remarks:
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.sp
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It is no problem to mix different compression methods in one repo,
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deduplication is done on the source data chunks (not on the compressed
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or encrypted data).
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.sp
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If some specific chunk was once compressed and stored into the repo, creating
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another backup that also uses this chunk will not change the stored chunk.
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So if you use different compression specs for the backups, whichever stores a
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chunk first determines its compression. See also borg recreate.
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.SH AUTHOR
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The Borg Collective
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.\" Generated by docutils manpage writer.
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.
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