Tangential to this when are operating systems going to ship w/ CoW filesystems by default? Accidental deletion of critical directories has been a solved problem for years now. I take instant snapshots of my home directory on ZFS every hour, my boot environment is snapshotted before every update.

You could literally remove my entire root directory and at worst you've minorly inconvenienced me: I now have to boot from a USB drive and run `zfs rollback` to the most recent snapshot. I'd be impervious to most ransomware as well: my home directory is filled w/ garbage now? Good thing it can't encrypt my read only snapshots, even with root access. Oh and I can serialize those snapshots across the network at the block level before I nuke the infected machine.

Of course humanity will always invent a bigger idiot, so it's possible a virus could gain root & exec some dangerous ZFS commands, or it's possible some MSFT employee could pass the `-r` flag and recursively delete a dataset & its snapshots in their post-update script. Plus let's not forget that no filesystem in the world will stop you from just zero-filling the drive. Still it's easy for me to imagine a world where I'm completely impervious from ransomware: by way of only being able to delete critical snapshots when a hardware key is present or when my TPM is unlocked.

On the whole it seems to me CoW filesystems are a major step forward in safe-guarding users from accidental deletions. At a minimum they have other benefits (serialized incremental send streams, block level compression & dedup, etc.) that make backups easier to manage. -- Yet I still can't boot from ReFS on Windows.