Date: Wed, 1 Feb 2012 11:45:21 -0500
From: Chris Mason <chris.mason@oracle.com>
To: Gregory Farnum <gregory.farnum@dreamhost.com>
Cc: Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        linux-scsi@vger.kernel.org,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Sven Breuner <sven.breuner@itwm.fraunhofer.de>,
        Chuck Lever <chuck.lever@oracle.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        lsf-pc@lists.linux-foundation.org
Subject: Re: [Lsf-pc] [LSF/MM TOPIC] end-to-end data and metadata corruption
 detection
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On Tue, Jan 31, 2012 at 11:28:26AM -0800, Gregory Farnum wrote:
> On Tue, Jan 31, 2012 at 11:22 AM, Bernd Schubert
> <bernd.schubert@itwm.fraunhofer.de> wrote:
> > I guess we should talk to developers of other parallel file systems and see
> > what they think about it. I think cephfs already uses data integrity
> > provided by btrfs, although I'm not entirely sure and need to check the
> > code. As I said before, Lustre does network checksums already and *might* be
> > interested.
> 
> Actually, right now Ceph doesn't check btrfs' data integrity
> information, but since Ceph doesn't have any data-at-rest integrity
> verification it relies on btrfs if you want that. Integrating
> integrity verification throughout the system is on our long-term to-do
> list.
> We too will be said if using a kernel-level integrity system requires
> using DIO, although we could probably work out a way to do
> "translation" between our own integrity checksums and the
> btrfs-generated ones if we have to (thanks to replication).

DIO isn't really required, but doing this without synchronous writes
will get painful in a hurry.  There's nothing wrong with letting the
data sit in the page cache after the IO is done though.

-chris