[mort96]

For apps which write a new file and replace atomically, the CoW mechanism doesn't come into play at all. The new file is a new file.

I don't understand what makes you think there's a significant risk of corruption. Are you talking about the risk of something modifying a file while the dedupe is happening? Or do you think there's risk associated with just having deduplicated files on disk?

[jonhohle]

The vast majority of apps using structured data and not block oriented data formats. A major exception is databases, but common file formats that most people work with - images, text, etc. often aren't best mutated directly on disk, but rewritten either to the same file or a new file. Without some transactional capability, mutating a file directly on disk can corrupt a file if the writer fails in the middle of the write. More than a few text editors use this as their method of saving to ensure that there is never an inconsistent state of that file on disk.