From: Hugo Mills <hugo@carfax.org.uk>
To: Andreas Grosse <andig.listen@aol.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: Incompat features: raid56 ... when creating a RAID6?
Date: Tue, 15 Mar 2016 22:06:11 +0000 [thread overview]
Message-ID: <20160315220611.GL17196@carfax.org.uk> (raw)
In-Reply-To: <16570443.SxVegaKaET@andilaptop>
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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.
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next prev parent reply other threads:[~2016-03-15 22:06 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-15 21:42 Incompat features: raid56 ... when creating a RAID6? Andreas Grosse
2016-03-15 22:06 ` Hugo Mills [this message]
2016-03-15 22:19 ` Anand Jain
2016-03-15 23:51 ` Andreas Grosse
2016-03-16 0:52 ` Anand Jain
2016-03-16 9:12 ` Andreas Grosse
2016-03-17 7:55 ` Duncan
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