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On Sat, Nov 26, 2011 at 8:39 PM, Michał Górny <mgorny@g.o> wrote: |
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> But in this particular case, I don't think COW is particularly useful. |
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> If it works only on filesystem bounds, we could move the file directly |
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> anyway. |
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> |
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There are still a few specific cases in which CoW would indeed be |
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useful. IIRC, reflinking of files works across btrfs *subvolumes*, and |
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such a copy would normally be detected as a cross-device move. Another |
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use would be an patch-merge which makes use of *ranged reflinks* to |
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only CoW copy those parts of the file that were changed[1]. rsync has |
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support for this, but only while appending to files (--append-verify |
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--no-whole-file). |
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1. Somewhat like rope data structures, with the caveat that ranges |
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must be block-size aligned. |
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-- |
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~Nirbheek Chauhan |
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Gentoo GNOME+Mozilla Team |