Chris Murphy posted on Wed, 01 Mar 2017 17:30:37 -0700 as excerpted: > [1717713.408675] BTRFS warning (device dm-8): missing devices (1) > exceeds the limit (0), writeable mount is not allowed > [1717713.446453] BTRFS error (device dm-8): open_ctree failed > > [chris@f25s ~]$ uname > -r 4.9.8-200.fc25.x86_64 > > I thought this was fixed. I'm still getting a one time degraded rw > mount, after that it's no longer allowed, which really doesn't make any > sense because those single chunks are on the drive I'm trying to mount. > I don't understand what problem this proscription is trying to avoid. If > it's OK to mount rw,degraded once, then it's OK to allow it twice. If > it's not OK twice, it's not OK once. AFAIK, no, it hasn't been fixed, at least not in mainline, because the patches to fix it got stuck in some long-running project patch queue (IIRC, the one for on-degraded auto-device-replace), with no timeline known to me on mainline merge. Meanwhile, the problem as I understand it is that at the first raid1 degraded writable mount, no single-mode chunks exist, but without the second device, they are created. (It's not clear to me whether they are created with the first write, that is, ignoring any space in existing degraded raid1 chunks, or if that's used up first and the single-mode chunks only created later, when a new chunk must be allocated to continue writing as the old ones are full.) So the first degraded-writable mount is allowed, because no single-mode chunks yet exist, while after such single-mode chunks are created, the existing dumb algorithm won't allow further writable mounts, because it sees single-mode chunks on a multi-device filesystem, and never mind that all the single mode chunks are there, it simply doesn't check that and won't allow writable mount because some /might/ be on the missing device. The patches stuck in queue would make btrfs more intelligent about that, having it check each chunk as listed in the chunk tree, and if at least one copy is available (as would be the case for single-mode chunks created after the degraded mount), writable mount would still be allowed. But... that's stuck in a long running project queue with no known timetable for merging... <grumble, grumble>... so the only way to get it is to go find and merge them yourself, in your own build. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- 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
