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Re: Debunking myths about metadata CRC overhead

To: Ben Myers <bpm@xxxxxxx>
Subject: Re: Debunking myths about metadata CRC overhead
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 5 Jun 2013 08:06:10 +1000
Cc: Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130604162030.GJ20932@xxxxxxx>
References: <20130603074452.GZ29466@dastard> <20130603111011.461d10b5@xxxxxxxxxxxxxx> <20130604025307.GB29466@dastard> <20130604162030.GJ20932@xxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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?


Dave Chinner

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