Re: Debunking myths about metadata CRC overhead

From: Chandra Seetharaman <sekharan@us.ibm.com>
To: Dave Chinner <david@fromorbit.com>
Cc: xfs@oss.sgi.com
Subject: Re: Debunking myths about metadata CRC overhead
Date: Tue, 04 Jun 2013 17:40:16 -0500	[thread overview]
Message-ID: <1370385616.22504.7.camel@chandra-dt.ibm.com> (raw)
In-Reply-To: <20130604220849.GK29466@dastard>

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 ?

> > 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
> it.
> 

Thanks.
> Cheers,
> 
> Dave.

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