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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 08:59:35 +1000
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1370385616.22504.7.camel@xxxxxxxxxxxxxxxxxx>
References: <20130603074452.GZ29466@dastard> <20130603111011.461d10b5@xxxxxxxxxxxxxx> <20130604025307.GB29466@dastard> <1370371109.3898.10.camel@xxxxxxxxxxxxxxxxxx> <20130604220849.GK29466@dastard> <1370385616.22504.7.camel@xxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Jun 04, 2013 at 05:40:16PM -0500, Chandra Seetharaman wrote:
> On Wed, 2013-06-05 at 08:08 +1000, Dave Chinner wrote:
> > 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.
> > 
> 
> Oh, I see. It is clear now.
> 
> Also, is there a git tree where I can pull your xfsprogs changes from ?
> I tried to apply xfsprogs-kern-sync-patchset-v2.tar.gz on top of
> xfsprogs git tree, it seems to have some problems.
> 
> Or is there a later version ?

I'm cleaning up my current tree right now. I'll post it out as soon
as it is ready to go. Hopefully Ben can get that into a branch in
the xfsprogs git tree and you can pull from there.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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