43 lines
2.1 KiB
Markdown
43 lines
2.1 KiB
Markdown
git-annex uses a key-value abstraction layer to allow file contents to be
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stored in different ways. In theory, any key-value storage system could be
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used to store file contents.
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When a file is annexed, a key is generated from its content and/or metadata.
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The file checked into git symlinks to the key. This key can later be used
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to retrieve the file's content (its value).
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Multiple pluggable backends are supported, and a single repository
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can use different backends for different files.
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These backends can transfer file contents between configured git remotes.
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It's also possible to use [[special_remotes]], such as Amazon S3 with
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these backends.
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* `WORM` ("Write Once, Read Many") This backend assumes that any file with
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the same basename, size, and modification time has the same content. So with
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this backend, files can be moved around, but should never be added to
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or changed. This is the default, and the least expensive backend.
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* `SHA1` -- This backend uses a key based on a sha1 checksum. This backend
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allows modifications of files to be tracked. Its need to generate checksums
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can make it slower for large files.
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* `SHA512`, `SHA384`, `SHA256`, `SHA224` -- Like SHA1, but larger
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checksums. Mostly useful for the very paranoid, or anyone who is
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researching checksum collisions and wants to annex their colliding data. ;)
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* `SHA1E`, `SHA512E`, etc -- Variants that preserve filename extension as
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part of the key. Useful for archival tasks where the filename extension
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contains metadata that should be preserved.
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The `annex.backends` git-config setting can be used to list the backends
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git-annex should use. The first one listed will be used by default when
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new files are added.
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For finer control of what backend is used when adding different types of
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files, the `.gitattributes` file can be used. The `annex.backend`
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attribute can be set to the name of the backend to use for matching files.
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For example, to use the SHA1 backend for sound files, which tend to be
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smallish and might be modified over time, you could set in
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`.gitattributes`:
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*.mp3 annex.backend=SHA1
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*.ogg annex.backend=SHA1
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