Simon Waid posted on Mon, 23 Jan 2017 09:42:28 +0100 as excerpted:
> I have a btrfs raid5 array that has become unmountable. [As a list regular and btrfs user myself, not a dev, but I try to help with replies where I can in ordered to allow the devs and real experts to put their time to better use where I can't help.] As stated on the btrfs wiki and in the mkfs.btrfs manpage, btrfs raid56 hasn't stabilized and is now known to have critical defects as originally implemented, that make it unfit for the purposes most people normally use parity-raid for. It's not recommended except for testing with purely sacrificial data that might potentially be eaten by the test. Thus, anyone on btrfs raid56 mode should only been testing with effectively throw-away data, either because it's backed up and can be easily retrieved from that backup, or because it really /is/ throw-away data, making the damage from losing that testing filesystem minimal. As such, if you're done with testing, the fastest and most efficient way back to production is to forget about the broken filesystem, and blow it away with a mkfs to a new filesystem, either some other btrfs mode or something other than the still maturing btrfs entirely, your choice. Then you can restore from backups if the data was worth having them. Tho of course blowing it away does mean it can't be used as a lab specimen to perhaps help find and fix some of the problems that do affect raid56 mode at this time. Qu Wenruo in particular, and others, have been gradually working thru at least some of the raid56 mode bugs, tho it's still possible the current code is beyond hope and may need entirely rewritten to properly stabilize. If you don't have to get the space the filesystem was taking directly back in service and can build and work with the newest code possibly including patches they ask you to apply, you may be able to use your deployment as a lab specimen to help them test their newest recovery code and possibly help fix additional bugs in the process. However, even then, don't expect that you'll necessarily recover most of what was on the filesystem, as raid56 mode really is seriously bugged ATM, and it's quite possible that the data has already been wiped out by those bugs. Mostly, you're simply continuing to use the filesystem as an in-the-wild test deployment gone bad, now testing diagnostics and possible recovery, not necessarily with a good chance of recovering the data, but that's OK, since btrfs raid56 mode was never out of unstable testing-only mode in the first place, so any data put on it always was effectively sacrificial data, known to be potentially eaten by the testing itself. -- 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
