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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: Chandra Seetharaman <sekharan@xxxxxxxxxx>
Date: Tue, 04 Jun 2013 13:38:29 -0500
Cc: Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130604025307.GB29466@dastard>
Organization: IBM
References: <20130603074452.GZ29466@dastard> <20130603111011.461d10b5@xxxxxxxxxxxxxx> <20130604025307.GB29466@dastard>
Reply-to: sekharan@xxxxxxxxxx
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 Ãcriviez:
> > 
> > > 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....


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). 

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.


> Cheers,
> Dave

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