> You do know how journalling works, yes? Unless the drive lies about the state of data being written, in which case not even COW will save you, a journal is just as good as COW. Exceptions being coding errors but those can occur on COW with the same devastating result.

Yes, I'm aware of how journaling works. The problem with your description is that it requires both data and metadata journaling. This is rarely the case because data journaling requires that you write all of your data to the disk twice (which also requires additional seeks as well). So, nearly all in-place filesystems default to only metadata journaling for performance reasons (this is the case for ext4). This means that, in practice, if you get a system crash mid file write, you will end up with a partially updated file. On a COW filesystem you are always guaranteed the old file or the new file.

> Maybe you don't know as much about filesystems as you want to appear to?

That is possible, although I'm not sure how much I want to appear to know :P. More seriously, this is extremely condescending. Why is this necessary? If you think I'm wrong, just tell me I'm wrong. There is a pretty decent chance I'm wrong about most things. So, condescension shouldn't be required.