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List:       linux-btrfs
Subject:    Re: BUG: >16TB Btrfs volumes are mountable on 32 bit kernels
From:       Josef Bacik <jbacik () fb ! com>
Date:       2014-02-28 13:05:21
Message-ID: 53108991.4030504 () fb ! com
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On 02/27/2014 11:38 PM, Dave Chinner wrote:
> On Thu, Feb 27, 2014 at 04:07:06PM -0500, Josef Bacik wrote:
> > -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
> > 
> > On 02/27/2014 04:05 PM, Chris Murphy wrote:
> > > User reports successfully formatting and using an ~18TB Btrfs 
> > > volume on hardware raid5 using i686 kernel for over a year,
> > > and then suddenly the file system starts behaving weirdly:
> > > 
> > > https://urldefense.proofpoint.com/v1/url?u=http://www.mail-archive.com/linux-btr \
> > > fs%40vger.kernel.org/msg31856.html&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=cKCbChRKs \
> > > MpTX8ybrSkonQ%3D%3D%0A&m=6eUt5RgBggFh930oFrH19iR4z%2BFVzT%2F0%2F4dYPt3g48U%3D%0A&s=5ac126734d7fa1d3238ab09a2ddc021a8dcc8fff7b022560a4d068be2de37c00
> > >  
> > > 
> > > 
> > > 
> > > 
I think this is due to the kernel page cache address space being
> > > 16TB limited on 32-bit kernels, as mentioned by Dave Chinner
> > > in this thread:
> > > 
> > > https://urldefense.proofpoint.com/v1/url?u=http://oss.sgi.com/pipermail/xfs/2014 \
> > > -February/034588.html&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=cKCbChRKsMpTX8ybrSkonQ \
> > > %3D%3D%0A&m=6eUt5RgBggFh930oFrH19iR4z%2BFVzT%2F0%2F4dYPt3g48U%3D%0A&s=3e45f9288e6a77bc1a24dded368802c2ab46b812bf59953f74d4ee1d4141f7d2
> > >  
> > > 
> > > 
So it sounds like it shouldn't be possible to mount a Btrfs volume
> > > larger than 16TB on 32-bit kernels. This is consistent with
> > > ext4 and XFS which refuse to mount large file systems.
> > > 
> > > 
> > 
> > Well that's not good, I'll fix this up.  Thanks,
> 
> Well, don't go assuming there's a problem just because I made an 
> off-hand comment. i.e my comment was simply "maybe it hasn't been 
> tested", and not an assertion that there is a bug or a problem....
> 

If I can't take your word as gospel then my whole life has been a lie!
 I'll look into it some more then but I seem to remember this being a
real problem, like we'd wrap around in pagecache once we went above
16tb, which would cause problems for metadata since our btree inode is
mapped logically to the entire fs.  Thanks,

Josef

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