RE: 4.1 no-pnfs mount option?

[Trond Myklebust <Trond.Myklebust@netapp.com>]

On Tue, 2011-01-18 at 21:29 -0500, Daniel.Muntz@emc.com wrote: 
> 
> > -----Original Message-----
> > From: Trond Myklebust [mailto:Trond.Myklebust@netapp.com] 
> > Sent: Tuesday, January 18, 2011 5:45 PM
> > To: Muntz, Daniel
> > Cc: matt@linuxbox.com; rees@umich.edu; 
> > androsadamson@gmail.com; linux-nfs@vger.kernel.org; 
> > bhalevy@panasas.com
> > Subject: RE: 4.1 no-pnfs mount option?
> > 
> > On Tue, 2011-01-18 at 19:53 -0500, Daniel.Muntz@emc.com wrote: 
> > > 
> > > > -----Original Message-----
> > > > From: Trond Myklebust [mailto:Trond.Myklebust@netapp.com] 
> > > > Sent: Tuesday, January 18, 2011 11:15 AM
> > > > To: Matt W. Benjamin
> > > > Cc: Muntz, Daniel; rees@umich.edu; androsadamson@gmail.com; 
> > > > linux-nfs@vger.kernel.org; Benny Halevy
> > > > Subject: Re: 4.1 no-pnfs mount option?
> > > > 
> > > > On Tue, 2011-01-18 at 13:46 -0500, Matt W. Benjamin wrote: 
> > > > > Hi,
> > > > > 
> > > > > Isn't by mount a plausible way to select for pnfs 
> > > > independent of debugging?  Is it assured that a client 
> > > > administrator would never reasonably wish to do this?
> > > > 
> > > > "Why would an administrator never want to do this?" is 
> > not a helpful
> > > > question.
> > > > 
> > > > A more useful question is "what reason would you possibly have for
> > > > overriding the server's request that you do pNFS when 
> > your client has
> > > > pNFS support?" What makes pNFS so special that we must allow
> > > > administrators to do this on a per-mount basis?
> > > 
> > > By the same logic, why should a user be allowed to select 
> > which version of NFS they use for mounting when the server 
> > has a perfectly reasonable way of negotiating it?  Getting to 
> > choose v2 vs. v3 vs. v4 seems like much less of a distinction 
> > than choosing between pNFS and no pNFS.  Frankly, it never 
> > even occurred to me that there wouldn't be a mount option to 
> > make this choice.  Enabling/disabling the layout driver 
> > doesn't fit the existing model of choosing mount behavior, 
> > and is a big hammer--it's all or nothing.
> > > 
> > > Anyway, here's a use case: I'm working at an 
> > HPC/gas+oil/satellite data site.  We have an awesome pNFS 
> > server for our big data and I want to access my big data with 
> > pNFS.  We have another server for homedirs, some big data, 
> > and other stuff.  Some mounts are fine with pNFS, others are 
> > abysmal.  So, I want to mount some directories with pNFS, and 
> > some without pNFS, on the same client, independent of the 
> > server configuration.
> > 
> > mount -t nfs -overs=4,minorversion=0 foo:/ /bar
> > 
> > Done... Any more questions?
> 
> Several, but I'll stick to one rhetorical.  Does NFSv4.1 have any features, other than pNFS, that are not in 4.0?

Why stop now, when you were batting 100? I told you what the criteria
were for adding more mount options, and you start whining about not
being able to conceive of a world without mount options.

The point is that NFSv4.1 was supposed to let the _server_ tell the
client when to use pNFS. The reason why you let the _server_ do this, is
because pNFS is about enabling _server_ scalability. It is not about
faster clients...
If you don't want the client to use pNFS, then fix the _server_
settings...

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com