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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"shutil.copyfile should use ReFS block-level linking on Windows (by invoking CopyFileW)","articleBody":"# Bug report\n\n### Bug description:\n\n```python\nshutil.copyfile(\"./scratch.txt\", \"./target.txt\")\n```\n\ncopyfile for copies within a single ReFS volume (or Dev Drive) on Windows 11 does not take advantage of block-level linking capability present in ReFS file system. On the other hand, the kernel automatically does so when you invoke CopyFileW these days. C#/.NET use kernel functions for file copy APIs and automatically take advantage of this too.\n\nPython does not offer an API that takes advantage of block-level linking except for directly invoking CopyFileW using windlls.kernel32 from ctypes.\n\nhttps://docs.python.org/3/library/shutil.html#shutil-platform-dependent-efficient-copy-operations\nCopyFileW should be used instead of streaming data from one file to another, at least in circumstances where block-level linking is possible.\n\nRelevant code: https://github.com/python/cpython/blob/e93c30d4666f925c6a5a2cc4952f69782760d101/Lib/shutil.py#L313\n\n### CPython versions tested on:\n\n3.9\n\n### Operating systems tested on:\n\nWindows","author":{"url":"https://github.com/Dico200","@type":"Person","name":"Dico200"},"datePublished":"2025-07-24T11:51:35.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/137074/cpython/issues/137074"}