With SSD it's common that they start returning zeros or garbage, sometimes transiently, before they fail. In the case of single device Btrfs, it basically acts

With SSD it's common that they start returning zeros or garbage, sometimes transiently, before they fail. In the case of single device Btrfs, it basically acts as an early warning detection system, and it will be a lot more sensitive to this than other file systems because both metadata (the fs itself) and your data, are checksummed. And the data is a much bigger portion of the payload on your drive. It's way more likely to be hit by hardware related issues, including even memory bit flips. An inability to mount Btrfs means metadata has been hit by some kind of corruption, and there are more structures in Btrfs that are critical. If they're hit, you see mount failure. And repair can be harder on Btrfs as well. But it also has a lot more opportunities for recovery that aren't very well understood or discussed. In part because very serious problems like this aren't that common. And also, quite a lot of people give up. Maybe they have backups and just start over with a new file system and restore. Or through no fault of their own they don't persevere with 'btrfs restore' - which is a very capable tool but requires specialized knowledge right now to use it effectively. One of the things that'll take a mindset shift is the idea of emphasizing recoveries over repairs. One improvement coming soonish (hopefully end of the year) is more tolerant read-only rescue mount option, making it possible for users to recover with normal tools rather than 'btrfs restore'.