Chris Murphy posted on Fri, 25 Mar 2016 15:34:11 -0600 as excerpted: > Basically you get one chance to mount rw,degraded and you have to fix > the problem at that time. And you have to balance away any phantom > single chunks that have appeared. For what it's worth it's not the > reboot that degraded it further, it's the unmount and then attempt to > mount rw,degraded a 2nd time that's not allowed due to this bug.
As CMurphy says here but without mentioning the patch, as Alexander F says in sibling to CMurphy's reply, and as I said in my longer explanation further upthread, this is a known bug, with a patch in the pipeline that really should have made it into 4.5 but didn't as it was part of a larger patch set that apparently wasn't considered ready, and unfortunately it wasn't cherrypicked. So right now, yes, known bug. You get one chance at a degraded-writable mount to rebuild the array. If you crash after writing but before the rebuild is complete, too bad, so sad, now you can only mount degraded- readonly and your only possibility of saving the data (other than rebuilding with the appropriate patch) is to do just that, mount degraded- readonly, and copy off the data to elsewhere. But there's a patch that has been demonstrated to fix the bug, not only in tests, but in live-deployments where people found themselves with a degraded-readonly mount until they built with the patch. Hopefully that patch will hit the 4.6 development kernel with a CC to stable, and be backported as necessary there, but I'm not sure it will be in 4.6 at this point, tho it should hit mainline /eventually/. Meanwhile, the patch can still be applied manually if necessary, and I suppose some distros may already be applying it to their shipped versions as it's certainly a fix worth having. I'll simply refer you to previous discussion on the list for the patch, as that's where I'd have to look for it if I needed it myself before it gets mainlined. -- 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
