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The nice feller over at phoronix brings us this handy to have bit of info:
It turns out the RAID5 and RAID6 code for the Btrfs file-system's built-in RAID support is faulty and users should not be making use of it if you care about your data.
There has been this mailing list thread since the end of July about Btrfs scrub recalculating the wrong parity in RAID5. The wrong parity and unrecoverable errors has been confirmed by multiple parties. The Btrfs RAID 5/6 code has been called as much as fatally flawed -- "more or less fatally flawed, and a full scrap and rewrite to an entirely different raid56 mode on-disk format may be necessary to fix it. And what's even clearer is that people /really/ shouldn't be using raid56 mode for anything but testing with throw-away data, at this point. Anything else is simply irresponsible."
Just as well I haven't gotten around to trying it then.
(Score: 4, Interesting) by Marand on Sunday August 07 2016, @05:54PM
(Oracle owns ZFS and is also the chief contributor to btrfs)
Sounds like this might be part of the problem. Oracle started Btrfs in 2007, then acquired Sun (and ZFS) in 2010. Once Oracle became the owner of the filesystem they were trying to ape, what reason was there to continue putting heavy development into Btrfs?
Sure, Oracle kept some token effort going on there, but the incentive to make it usable for their needs died once they became owner of the filesystem they were trying to ape, and most everyone else seems to be fine using ZFS, ext3/4, or one of the others like XFS.
(Score: 1) by Francis on Sunday August 07 2016, @09:33PM
Apart from the nutters that insist upon using draconian licensing schemes to control developer behavior, was there every really any point to the filesystem? It seems to me that the problem with Linux filesystems isn't that there are too few of them, but that there's so many that they often times aren't completed before being incorporated. I'm still allergic to EXT4 because when I first tried using it, it would eat the entire install if the system crashed. And the system crashed every time I loaded it, so I'd have to reinstall every single time I'd want to use it.
Needless to say, I stopped using it and avoid it like the plague, but having a ton of filesystems available that aren't necessarily read for primetime isn't really a good idea. On some level if a filesystem isn't production ready after a certain number of years, it's probably not going to be ready ever. Either it's too niche to attract developers or it's gone off the rails by trying to do too much.
(Score: 0) by Anonymous Coward on Sunday August 07 2016, @09:57PM
crashing an ext4 filesystem by having your seagate harddrive overheat does the same thing.
And yes I have tried with ext2/3 and the same thing doesn't happen... HOWEVER running ext3 on the ext4 driver DOES cause similiar corruption.
So now all my archival partitions stay ext2 and only my OS drives end up ext4 (it does offer better performance usually, but the reliability is definitely shite. Plus it is unreliable thanks to feature changes if you ever need to use it in a system with an older kernel! Same deal with ext2 if you aren't careful about mkfs options!) Another issue to be aware of: the ext3 driver breaks on certain options depending on if you're using an i686 vs an x86_64 driver. The ext4 driver will load the i686 formatted partitions on x86_64, but will if you switch to an i686 kernel, whereas the ext3 driver (when still present in the kernel) would load the partition on i686 but fail if you attempted to load it on x86_64 with an invalid filesystem options error. Why is this important? Because it meant either changing the fstab entry before boot, or manually setting the filesystem driver on the kernel commandline to ensure it would boot smoothly. Forget to do it, especially on a remote system, and you end up with your server hung.
(Score: 2) by Marand on Sunday August 07 2016, @11:10PM
Apart from the nutters that insist upon using draconian licensing schemes to control developer behavior, was there every really any point to the filesystem?
It started inside Oracle, so the reasoning was probably as simple as "Oracle wanted ZFS but Sun has it." No idea why they didn't just abandon ship as soon as they bought Sun, though; maybe a passionate dev in the company convinced someone to keep working on it fort he future or something.
The appeal for others was either "ZFS licensing isn't compatible with the Linux kernel but we want ZFS features" or "we want stuff that ext[2|3|4] doesn't have", but it's apparently not been enough. It may well be a good long term goal, and if that's what someone wants to work on good for them, but it still isn't ready for everyday use and I'm amazed people actually suggest it for such. :/
I've got nothing against developing new filesystems, and I don't think it's a problem that the kernel supports a bunch of niche ones, because use cases are different and sometimes a good specialised FS isn't suitable for general use (or vice-versa). The problem here with btrs is that filesystems are too damn important to put into production use when still immature, and for whatever reason people seem to think it's production-ready when it's clearly not.