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Re: Debunking myths about metadata CRC overhead

To: Chandra Seetharaman <sekharan@xxxxxxxxxx>
Subject: Re: Debunking myths about metadata CRC overhead
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 5 Jun 2013 08:08:49 +1000
Cc: Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1370371109.3898.10.camel@xxxxxxxxxxxxxxxxxx>
References: <20130603074452.GZ29466@dastard> <20130603111011.461d10b5@xxxxxxxxxxxxxx> <20130604025307.GB29466@dastard> <1370371109.3898.10.camel@xxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Jun 04, 2013 at 01:38:29PM -0500, Chandra Seetharaman wrote:
> On Tue, 2013-06-04 at 12:53 +1000, Dave Chinner wrote:
> > On Mon, Jun 03, 2013 at 11:10:11AM +0200, Emmanuel Florac wrote:
> > > Le Mon, 3 Jun 2013 17:44:52 +1000 vous écriviez:
> > > 
> > > > There has been some assertions made recently that metadata CRCs have
> > > > too much overhead to always be enabled.  So I'll run some quick
> > > > benchmarks to demonstrate the "too much overhead" assertions are
> > > > completely unfounded.
> > > 
> > > Just a quick question: what is the minimal kernel version and xfsprogs
> > > version needed to run xfs with metadata CRC? I'd happily test it on
> > > real hardware, I have a couple of storage servers in test in the 40 to
> > > 108 TB range.
> > 
> > If the maintainers merge all the patches I send for the 3.10-rc
> > series, then the 3.10 release should be stable enough to use for
> > testing with data you don't care if you lose.
> > 
> > As for the userspace code - that is still just a patchset. I haven't
> > had any feedback from the maintainers about it in the past month, so
> > I've got no idea what they are doing with it. I'll post out a new
> > version in the next couple of days - it's 50-odd patches by now, so
> > it'd be nice to have it in the xfsprogs git tree so people could
> > just pull it and build it for testing purposes by the time that 3.10
> > releases....
> Dave,
> I was of the impression that the user space changes will be released
> sometime later (i.e when CRC comes out of experimental). If we make the
> user space changes to create V5 filesystem now, it will be an annoyance
> for people that created V5 super blocks without my changes (getting rid
> of OQUOTA.* flags). 

People still need access to the code to test it. I'm not talking
about an official release here at all, just getting it committed to
the git tree to make it easy for people to get the code and for
developers to build on top of it and fix bugs.

> BTW, I am waiting for your response to do a final re-post on the kernel
> changes, after which I will post my user space changes.

I must have missed your question, I'll go back and have a look for


Dave Chinner

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