Thanks Chris for the warning. I agree that mounting both drives separately in degraded r/w will lead to very funky results when trying to scrub them when put together. On Mon, Jan 4, 2016 at 6:41 PM, Chris Murphy <lists@xxxxxxxxxxxxxxxxx> wrote: > On Mon, Jan 4, 2016 at 10:00 AM, Alphazo <alphazo@xxxxxxxxx> wrote: > >> I have tested the above use case with a couple of USB flash drive and >> even used btrfs over dm-crypt partitions and it seemed to work fine >> but I wanted to get some advices from the community if this is really >> a bad practice that should not be used on the long run. Is there any >> limitation/risk to read/write to/from a degraded filesystem knowing it >> will be re-synced later? > > As long as you realize you're testing a sort of edge case, but an > important one (it should work, that's the point of rw degraded mounts > being possible), then I think it's fine. > > The warning though is, you need to designate a specific drive for the > rw,degraded mounts. If you were to separately rw,degraded mount the > two drives, the fs will become irreparably corrupt if they are > rejoined. And you'll probably lose everything on the volume. The other > thing is that to "resync" you have to manually initiate a scrub, it's > not going to resync automatically, and it has to read everything on > both drives to compare and fix what's missing. There is no equivalent > to a write intent bitmap on Btrfs like with mdadm (the information > ostensibly could be inferred from btrfs generation metadata similar to > how incremental snapshot send/receive works) but that work isn't done. > > > > > -- > Chris Murphy -- 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
