40 lines
2.0 KiB
ReStructuredText
40 lines
2.0 KiB
ReStructuredText
Inline files
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============
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Files up to some size can be stored in the metadata section ("inline" in the
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b-tree nodes), i.e. no separate blocks for the extents. The default limit is
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2048 bytes and can be configured by mount option ``max_inline``. The data of
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inlined files can be also compressed as long as they fit into the b-tree nodes.
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If the filesystem has been created with different data and metadata profiles,
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namely with different level of integrity, this also affects the inlined files.
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It can be completely disabled by mounting with ``max_inline=0``. The upper
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limit is either the size of b-tree node or the page size of the host.
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An inline file can be identified by enumerating the extents, e.g. by the tool
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:command:`filefrag`:
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.. code-block:: bash
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$ filefrag -v inlinefile
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Filesystem type is: 9123683e
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File size of inlinefile is 463 (1 block of 4096 bytes)
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ext: logical_offset: physical_offset: length: expected: flags:
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0: 0.. 4095: 0.. 4095: 4096: last,not_aligned,inline,eof
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In the above example, the file is not compressed, otherwise it would have the
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*encoded* flag. The inline files have no limitations and behave like regular
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files with respect to copying, renaming, reflink, truncate etc.
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.. note::
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This is not `tail packing <https://en.wikipedia.org/wiki/Block_suballocation#Tail_packing>`__,
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known e.g. from `ReiserFS <https://en.wikipedia.org/wiki/ReiserFS>`__ . The
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whole inline file must fit and is stored in the metadata block. Larger files
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have their extents stored in blocks and the last one can be underutilized.
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With tail packing such blocks would be stored elsewhere out of order,
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possibly mixed with other last blocks from other files.
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This was an early design decision not to implement it due to experience with
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the complexity in ReiserFS and does not seem justified with the possible
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space savings in the data blocks but increased metadata to track the packed blocks.
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