OK, let’s dive right into it. What happens when something goes wrong with a btrfs filesystem — or maybe you just suspect that something has gone wrong? Well, as I mentioned briefly in the second post in this series, you can use the btrfs scrub utility to read all of the data in the filesystem and verify the checksums as it goes.
Depending on the size of the filesystem, this can take a considerable time, so by default it will go off to do its work in the background and let you get on with other things on your terminal. Once you have a scrub running in the background, you can check on its progress at any time with the btrfs scrub status command. If it finds any checksum problems, the scrub process will attempt to repair them (unless you started it with the read-only option to suppress this).