On Tue, Mar 15, 2016 at 10:42:29PM +0100, Andreas Grosse wrote: > Hello everyone! > > I just wanted to create a RAID6 and got the following output: > > > # mkfs.btrfs -d raid6 -m raid6 -L slowPool /dev/sd[cdefgh] [snip] > > Incompat features: extref, raid56, skinny-metadata [snip] > And then the line saying "Incompat features: ... raid56" came to my eyes. > Reading the corresponding manpage, it says: > > raid56 > > extended format for RAID5/6, also enabled if raid5 or raid6 block groups > > are selected > So why is raid56 marked as incompatible if I just created a file system with > multiple disks using the RAID6 profile? Have I misunderstood something there? > I am confused. Can somebody here lighten this up?
It's a safety thing. The incompat flags are markers set in the filesystem to indicate which features that particular FS uses. Each kernel version has a list of features it can handle, and if it's asked to mount a filesystem with a feature that it doesn't recognise, it'll refuse to do so. So, you've created a filesystem with the RAID5/6 feature, it's marked as such in the FS (with the incompat flag "raid56"), and attempting to mount that FS on a kernel that doesn't know about parity RAID (earlier than 3.14, IIRC) will fail safely because the kernel can't handle it. Hugo. -- Hugo Mills | Alert status upwards vermilion: High probability of hugo@... carfax.org.uk | flash photography. Avoid wearing brogues. http://carfax.org.uk/ | PGP: E2AB1DE4 |
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