Could someone please point me towards some read about how btrfs handles multiple devices? Namely, kicking faulty devices and re-adding them.
I've been using btrfs on single devices for a while, but now I want to start using it in raid1 mode. I booted into an Ubuntu 17.10 LiveCD and tried to see how does it handle various situations. The experience left me very surprised; I've tried a number of things, all of which produced unexpected results. I create a btrfs raid1 filesystem on two hard drives and mount it. - When I pull one of the drives out (simulating a simple cable failure, which happens pretty often to me), the filesystem sometimes goes read-only. ??? - But only after a while, and not always. ??? - When I fix the cable problem (plug the device back), it's immediately "re-added" back. But I see no replication of the data I've written onto a degraded filesystem... Nothing shows any problems, so "my filesystem must be ok". ??? - If I unmount the filesystem and then mount it back, I see all my recent changes lost (everything I wrote during the "degraded" period). - If I continue working with a degraded raid1 filesystem (even without damaging it further by re-adding the faulty device), after a while it won't mount at all, even with "-o degraded". I can't wrap my head about all this. Either the kicked device should not be re-added, or it should be re-added "properly", or it should at least show some errors and not pretend nothing happened, right?.. I must be missing something. Is there an explanation somewhere about what's really going on during those situations? Also, do I understand correctly that upon detecting a faulty device (a write error), nothing is done about it except logging an error into the 'btrfs device stats' report? No device kicking, no notification?.. And what about degraded filesystems - is it absolutely forbidden to work with them without converting them to a "single" filesystem first?.. On Ubuntu 17.10, there's Linux 4.13.0-16 and btrfs-progs 4.12-1 . -- darkpenguin -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
