2021-12-09 19:46:42 +00:00
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Send/receive
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============
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2021-11-30 15:00:48 +00:00
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2021-12-09 19:46:42 +00:00
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Send and receive are complementary features that allow to transfer data from
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one filesystem to another in a streamable format. The send part traverses a
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given read-only subvolume and either creates a full stream representation of
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its data and metadata (*full mode*), or given a set of subvolumes for reference
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it generates a difference relative to that set (*incremental mode*).
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Receive on the other hand takes the stream and reconstructs a subvolume with
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files and directories equivalent to the filesystem that was used to produce the
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stream. The result is not exactly 1:1, eg. inode numbers can be different and
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other unique identifiers can be different (like the subvolume UUIDs). The full
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mode starts with an empty subvolume, creates all the files and then turns the
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subvolume to read-only. At this point it could be used as a starting point for a
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future incremental send stream, provided it would be generated from the same
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source subvolume on the other filesystem.
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The stream is a sequence of encoded commands that change eg. file metadata
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(owner, permissions, extended attributes), data extents (create, clone,
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truncate), whole file operations (rename, delete). The stream can be sent over
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network, piped directly to the receive command or saved to a file. Each command
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in the stream is protected by a CRC32C checksum.
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