27 lines
1.2 KiB
ReStructuredText
27 lines
1.2 KiB
ReStructuredText
Subpage support
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===============
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Subpage block size support, or just *subpage* for short, is a feature to allow
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using a filesystem that has different size of data block size (*sectorsize*)
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and the host CPU page size. For easier implementation the support was limited
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to the exactly same size of the block and page. On x86_64 this is typically
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4KiB, but there are other architectures commonly used that make use of larger
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pages, like 64KiB on 64bit ARM or PowerPC. This means filesystems created
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with 64KiB sector size cannot be mounted on a system with 4KiB page size.
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While with subpage support systems with 64KiB page size can create
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and mount filesystems with 4KiB sectorsize. This still needs to use option "-s
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4k" option for :command:`mkfs.btrfs`.
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Requirements, limitations
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-------------------------
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The initial subpage support has been added in v5.15, although it's still
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considered as experimental, most features are already working without problems.
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On a 64KiB page system filesystem with 4KiB sectorsize can be mounted and used
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as usual as long as the initial mount succeeds. There are cases a mount will be
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rejected when verifying compatible features.
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Please refer to status page of :ref:`status-subpage-block-size` for
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compatibility.
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