What ZFS does here is not enough for me. I need to be alerted to changes done also above the file system layer, like by malware or accidental deletion etc. Only way I have found to solve that is to have checksum tool above the file system. If something is wrong, I restore from backup, so zfs does not give me anything...
I don't personally do this, but if you're taking scheduled snapshots of your ZFS filesystems, you could also have a scheduled job (say, nightly) that emails you a "zfs diff" [0] between the current snapshot and the one from 24 hours ago. It won't tell you that you've been hit by malware, but an unexpected spike in changes could be something worth investigating.
As the name suggests, "snapshots" are read-only and so cannot be altered. You could either copy/rsync the modified file/s to the live location, or do a rollback to a particular snapshot:
You can clone the snapshot (so its clone become writable, not the snapshot itself!) and you even can promote a snapshot to a "parent" filesystem (reverse parent-child).
