36 lines
1.8 KiB
Markdown
36 lines
1.8 KiB
Markdown
The WORM and SHA1 key-value [[backends]] store data inside
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your git repository's `.git` directory, not in some external data store.
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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, then using those backends, 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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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.
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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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