Not all corruption is detectable. You could make a copy during a transaction where only a subset of the transactions saved pages are persisted but all branch & leaf pages are pointed to correctly. That would give you a state of the database that never actually existed and break atomicity.

> Not all corruption is detectable.

Well, I don't know rsync that well. If you're saying it doesn't detect changes to files while it's being copied, then I'll believe you.

And, as far as I know, it's impossible to detect absolutely all corruption.

But you can pretty easily detect, e.g., that a file has or has not changed since before you copied it to after, on a system with a basically functioning filesystem and clock, with a reasonable/useful level of confidence.