On Mon, Jan 4, 2016 at 10:00 AM, Alphazo <alph...@gmail.com> 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
