Marc MERLIN posted on Sat, 10 May 2014 16:57:18 -0700 as excerpted: > So, does scrub actually make sure everything on my filesystem is sane, > or can it miss some kinds of corruptions? Catching it here as well as the other thread... All scrub does is verify the checksum (and replace bad versions with good versions where there's a good copy available to do so). Scrub does NOT detect or fix faulty logic bug writes that never-the-less were properly checksummed, as the checksums can be perfectly valid on entirely invalid (meta)data. Using an example from recent US political history, it's as if someone recorded the head of the US NSA assuring congress that it did not knowingly collect data on US citizens in the generic case, when a few months later we found out it was doing just that. Now if that recording was checksummed, that checksum will normally still verify just fine today, even tho we know the claims in the recorded stream are 100% faulty. Verifying the checksum can validate the recording hasn't been corrupted since it was stored, but it does nothing at all to verify the claims made in that recording, and is simply the wrong tool for the job if that's what you're trying to do. Back on btrfs, if we were checksumming metadata and that metadata was faulty due to some now fixed bug, verifying the checksum simply verifies that the still-faulty metadata hasn't changed from when we stored it, not that the metadata isn't faulty in the first place. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
