On Thu, Mar 09, 2017 at 09:34:35AM +0800, Qu Wenruo wrote: > Btrfs currently uses num_tolerated_disk_barrier_failures to do global > check for tolerated missing device. > > Although the one-size-fit-all solution is quite safe, it's too strict > if data and metadata has different duplication level. > > For example, if one use Single data and RAID1 metadata for 2 disks, it > means any missing device will make the fs unable to be degraded > mounted. > > But in fact, some times all single chunks may be in the existing > device and in that case, we should allow it to be rw degraded mounted. > > Such case can be easily reproduced using the following script: > # mkfs.btrfs -f -m raid1 -d sing /dev/sdb /dev/sdc > # wipefs -f /dev/sdc > # mount /dev/sdb -o degraded,rw > > If using btrfs-debug-tree to check /dev/sdb, one should find that the > data chunk is only in sdb, so in fact it should allow degraded mount. > > This patchset will introduce a new per-chunk degradable check for > btrfs, allow above case to succeed, and it's quite small anyway. > > And enhance kernel error message for missing device, at least kernel > can know what's making mount failed, other than meaningless > "failed to read system chunk/chunk tree -5". I'd like to get this merged to 4.14. The flush bio changes are now done, so the base code should be stable. I've read the previous iterations of this patchset, the comments and user feedback. The usecase coverage seems to be good and what users expect. There are some bits in the implementation that I do not like, eg. reintroducing memory allocation failure to the barrier check, but IIRC no fundamental problems. Please refresh the patchset on top of current code that's going to 4.13 (equvalent to the current for-next), I'll review that and comment. One or more iterations might be needed, but 4.14 target is within reach. -- 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
