Kai Krakow posted on Thu, 02 Feb 2012 04:54:45 +0100 as excerpted: > Kai Krakow <[email protected]> schrieb: > >> Interestingly, the filesystem was not unmountable - system hung. After >> reisub and checking again with "btrfs scrub" no errors where reported >> and it just rsync'ed fine this time. This does not make sense to me. > > btrfsck still shows a lot of errors, while scrubbing says everything is > okay... *sigh > > Now, how should one fix it if there is still no repair utility? I'm > pretty sure sooner or later I will run into a BUG_ON again...
I had hoped someone else better qualified would answer, and they may still do so, but in the meantime, a couple notes... 1) This is unfortunately quite handwavy as I don't understand the details myself, but if I'm reading the list right, there's a known "phantom ENOSPC bug" that some are hitting when trying to write a large file (gigs, think dvd image), or do an rsync of several gigs, or... It may be that you hit it, and on retry, enough of the file was already there that it didn't trigger the second time around. I gather they've not traced what is apparently a timeout or race condition fully and are working on a temporary throttling-based workaround. That's supposed to work for the time being, but it's only a workaround, and the throttling controls themselves are apparently rather rough at this point, so part of the testing is to make it a bit easier for ordinary users without the esoteric knowledge of a btrfs dev to use. So there's a short-to-medium-term workaround coming and a longer term fix, once they trace down the problem itself. Meanwhile, don't be too worried about ENOSPC errors the occur under heavy write load and that go away on retry, as there's apparently others having the same issue. 2) Just a couple days ago I read an article that claimed Oracle has a Feb 16 deadline for a working btrfsck as that's the deadline for getting it in their next shipping Unbreakable Linux release. I won't claim to know if the article is correct or not, but if so, a reasonably working btrfsck should be available within two weeks. =:^) Of course it may continue to improve after that... Meanwhile, there's a tool already available that should allow retrieving the undamaged data off of unmountable filesystems, at least, and there's another tool that allows rollback to an earlier root node if necessary, thus allowing recovery of most filesystems at the cost of losing the last few seconds of work. Given the experimental nature of btrfs and the known lack of a proper btrfsck at this point anyway, that's... actually quite reasonable, and the reason I decided it was time to start checking out btrfs myself (I'm still researching but have been on the list about a week now and had read a couple weeks worth of posts before I responded to anything). Don't ask me what the names of those tools are. I could certainly look them up, but so can you, now that you know they exist. =:^) (assuming you didn't before, of course.) Hopefully that's somewhat helpful in pointing you in the right direction, at least. =:^) -- 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 [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
