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30 lines
1.4 KiB
ReStructuredText
30 lines
1.4 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 or 16KiB on Apple Silicon. This means
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filesystems created with 64KiB sector size cannot be mounted on a system with
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4KiB page size.
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Since btrfs-progs 6.7, filesystems are created with a 4KiB sector size by
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default, though it remains possible to create filesystems with other sector sizes
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(such as 64KiB with the "-s 64k" option for :command:`mkfs.btrfs`). This
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ensures that new filesystems are compatible across other architecture variants
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using larger page sizes.
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Requirements, limitations
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-------------------------
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The initial subpage support has been added in kernel 5.15. Most features are
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already working without problems. On a 64KiB page system, a filesystem with
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4KiB sectorsize can be mounted and used as long as the initial mount succeeds.
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Subpage support is used by default for systems with a non-4KiB page size since
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btrfs-progs 6.7.
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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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