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Re: Debunking myths about metadata CRC overhead

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: Debunking myths about metadata CRC overhead
From: Ben Myers <bpm@xxxxxxx>
Date: Tue, 4 Jun 2013 17:09:10 -0500
Cc: Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130604220610.GJ29466@dastard>
References: <20130603074452.GZ29466@dastard> <20130603111011.461d10b5@xxxxxxxxxxxxxx> <20130604025307.GB29466@dastard> <20130604162030.GJ20932@xxxxxxx> <20130604220610.GJ29466@dastard>
User-agent: Mutt/1.5.20 (2009-06-14)
On Wed, Jun 05, 2013 at 08:06:10AM +1000, Dave Chinner wrote:
> On Tue, Jun 04, 2013 at 11:20:30AM -0500, Ben Myers wrote:
> > Dave,
> > 
> > On Tue, Jun 04, 2013 at 12:53:07PM +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....
> > 
> > When it is reviewed and adequately tested we'll pull it in.  Until then
> > Emmanuel will need to pull down the patchset.  Right now the focus is on
> > 3.10.
> 
> And when will that be? I've already been waiting the best part of a
> month for anyone to even comment on it, and I've got 5 private pings
> in the past 3 days asking about how to get the userspace code so
> they can test the new kernel code....
> 
> How about this: I post an up-to-date patch set, and you guys commit
> it to a "crc-dev" branch in the oss xfsprogs git tree. The branch
> can be thrown away when the code is reviewed, but in the mean time
> we can point early adopters and testers to that branch rather than
> ask them to pull down and apply a 50 patch series to a git tree?

Sounds good to me.

-Ben

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