From: Dave Chinner <david@fromorbit.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>,
linux-xfs@vger.kernel.org
Subject: Re: Support for data CRC
Date: Mon, 11 Sep 2017 16:52:17 +1000 [thread overview]
Message-ID: <20170911065217.GQ17782@dastard> (raw)
In-Reply-To: <20170911063729.GA10489@infradead.org>
On Sun, Sep 10, 2017 at 11:37:29PM -0700, Christoph Hellwig wrote:
> On Sun, Sep 10, 2017 at 09:50:27PM +0200, Sebastian Andrzej Siewior wrote:
> > On 2017-08-22 23:19:31 [-0700], Christoph Hellwig wrote:
> > > as part of the reflink feature. These out of place writes are
> > > a requirement to implement data checksums, as otherwise your data
> > > and checksum can not be updated atomically. Everything else is
> > > beyond that at this point is vapourware. We'd have to decided
> > So using the journal for atomic updates doesn't work then. Which means
> > fragmentation unavoidable.
>
> Well, in theory you could also do data journalling - but in the end
> out of place writes are probably going to be more efficient, and at
> least for XFS also area already implemented.
>From a quick look at the dm-integrity code, it looks like it is just
a journalling block device. i.e. it logs both the data and the
calculated CRC in it's internal journal before writing the data and
CRC to their separate destinations so it can avoid inconsistent
data/CRCs if a crash occurs.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
prev parent reply other threads:[~2017-09-11 6:52 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-21 19:04 Support for data CRC Sebastian Andrzej Siewior
2017-08-21 19:52 ` Chris Murphy
2017-08-22 11:10 ` Sebastian Andrzej Siewior
2017-08-22 22:37 ` Chris Murphy
2017-09-10 19:43 ` Testing dm-integrity (WAS: Re: Support for data CRC) Sebastian Andrzej Siewior
2017-09-10 20:06 ` Milan Broz
2017-09-11 6:38 ` Sebastian Andrzej Siewior
2017-09-11 23:44 ` Mikulas Patocka
2017-08-21 23:02 ` Support for data CRC Dave Chinner
2017-08-22 5:51 ` Christoph Hellwig
2017-08-22 11:13 ` Sebastian Andrzej Siewior
2017-08-23 6:19 ` Christoph Hellwig
2017-09-10 19:50 ` Sebastian Andrzej Siewior
2017-09-11 6:37 ` Christoph Hellwig
2017-09-11 6:52 ` Dave Chinner [this message]
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