bbba6c19bd
Backends are now only used to generate keys (and check them); they are not arbitrary key-value stores for data, because it turned out such a store is better modeled as a special remote. Updated docs to not imply backends do more than they do now. Sometimes I'm tempted to rename "backend" to "keytype" or something, which would really be more clear. But it would be an annoying transition for users, with annex.backends etc.
38 lines
2 KiB
Markdown
38 lines
2 KiB
Markdown
Annexed data is stored inside your git repository's `.git/annex` directory.
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Some [[special_remotes]] can store annexed data elsewhere.
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It's important that data not get lost by an ill-considered `git annex drop`
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command. So, git-annex can be configured to try
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to keep N copies of a file's content available across all repositories.
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(Although [[untrusted_repositories|trust]] don't count toward this total.)
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By default, N is 1; it is configured by annex.numcopies. This default
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can be overridden on a per-file-type basis by the annex.numcopies
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setting in `.gitattributes` files. The --numcopies switch allows
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temporarily using a different value.
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`git annex drop` attempts to check with other git remotes, to check that N
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copies of the file exist. If enough repositories cannot be verified to have
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it, it will retain the file content to avoid data loss. Note that
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[[trusted_repositories|trust]] are not explicitly checked.
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For example, consider three repositories: Server, Laptop, and USB. Both Server
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and USB have a copy of a file, and N=1. If on Laptop, you `git annex get
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$file`, this will transfer it from either Server or USB (depending on which
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is available), and there are now 3 copies of the file.
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Suppose you want to free up space on Laptop again, and you `git annex drop` the file
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there. If USB is connected, or Server can be contacted, git-annex can check
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that it still has a copy of the file, and the content is removed from
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Laptop. But if USB is currently disconnected, and Server also cannot be
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contacted, it can't verify that it is safe to drop the file, and will
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refuse to do so.
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With N=2, in order to drop the file content from Laptop, it would need access
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to both USB and Server.
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Note that different repositories can be configured with different values of
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N. So just because Laptop has N=2, this does not prevent the number of
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copies falling to 1, when USB and Server have N=1. To avoid this,
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configure it in `.gitattributes`, which is shared between repositories
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using git.
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