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It seems to do COW and checksumming of metadata, but not of data. According to http://blogs.msdn.com/b/b8/archive/2012/01/16/building-the-n... there's a feature "integrity stream" which is opt-in per-file (or per-subtree and inherited by all files) checksumming. It doesn't seem to do COW, but can be paired with "storage spaces"[0] from which bitrotted files can be recovered.

[0] http://blogs.msdn.com/b/b8/archive/2012/01/05/virtualizing-s...

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Integrity streams are enabled by default on mirrored pools, as per your first link:

> By default, when the /i switch is not specified, the behavior that the system chooses depends on whether the volume resides on a mirrored space. On a mirrored space, integrity is enabled because we expect the benefits to significantly outweigh the costs.

Plus:

> When this option, known as “integrity streams,” is enabled, ReFS always writes the file changes to a location different from the original one. This allocate-on-write technique ensures that pre-existing data is not lost due to the new write

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