2010-10-19 19:59:40 +00:00
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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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2010-11-01 23:11:06 +00:00
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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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2010-10-19 19:59:40 +00:00
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* `WORM` ("Write Once, Read Many") This backend stores the file's content
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only in `.git/annex/`, and assumes that any file with the same basename,
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size, and modification time has the same content. So with this backend,
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files can be moved around, but should never be added to or changed.
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This is the default, and the least expensive backend.
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* `SHA1` -- This backend stores the file's content in
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`.git/annex/`, with a name based on its sha1 checksum. This backend allows
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modifications of files to be tracked. Its need to generate checksums
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2010-10-27 19:02:05 +00:00
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can make it slower for large files. **Warning** this backend is not ready
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for use.
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2010-10-19 19:59:40 +00:00
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* `URL` -- This backend downloads the file's content from an external URL.
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2010-11-01 23:11:06 +00:00
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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 `git-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 git-annex-backend=SHA1
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*.ogg git-annex-backend=SHA1
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