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On Fri, Sep 8, 2017 at 3:16 PM, Kai Krakow <hurikhan77@×××××.com> wrote: |
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> |
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> At least in btrfs there's also a caveat that the original extents may |
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> not actually be split and the split extents share parts of the |
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> original extent. That means, if you delete the original later, the copy |
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> will occupy more space than expected until you defragment the file: |
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> |
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True, but keep in mind that this applies in general in btrfs to any |
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kind of modification to a file. If you modify 1MB in the middle of a |
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10GB file on ext4 you end up it taking up 10GB of space. If you do |
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the same thing in btrfs you'll probably end up with the file taking up |
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10.001GB. Since btrfs doesn't overwrite files in-place it will |
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typically allocate a new extent for the additional 1MB, and the |
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original content at that position within the file is still on disk in |
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the original extent. It works a bit like a log-based filesystem in |
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this regard (which is also effectively copy on write). |
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-- |
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Rich |
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