Re: Distributed storage. Move away from char device ioctls.

Jeff Garzik
2007-09-15T04:08:56Z

J. Bruce Fields wrote:
> On Fri, Sep 14, 2007 at 06:32:11PM -0400, Jeff Garzik wrote:
>> J. Bruce Fields wrote:
>>> On Fri, Sep 14, 2007 at 05:14:53PM -0400, Jeff Garzik wrote:
>>>> NFSv4.1 adds to the fun, by throwing interoperability completely out the
>>>> window.

>>> What parts are you worried about in particular?

>> I'm not worried; I'm stating facts as they exist today (draft 13):
>>
>> NFS v4.1 does something completely without precedent in the history of NFS:
>> the specification is defined such that interoperability is -impossible- to
>> guarantee.
>>
>> pNFS permits private and unspecified layout types. This means it is
>> impossible to guarantee that one NFSv4.1 implementation will be able to
>> talk another NFSv4.1 implementation.

> No, servers are required to support ordinary nfs operations to the
> metadata server.
>
> At least, that's the way it was last I heard, which was a while ago. I
> agree that it'd stink (for any number of reasons) if you ever *had* to
> get a layout to access some file.
>
> Was that your main concern?

I just sorta assumed you could fall back to the NFSv4.0 mode of
operation, going through the metadata server for all data accesses.

But look at that choice in practice: you can either ditch pNFS
completely, or use a proprietary solution. The market incentives are
CLEARLY tilted in favor of makers of proprietary solutions. But it's a
poor choice (really little choice at all).

Overall, my main concern is that NFSv4.1 is no longer an open
architecture solution. The "no-pNFS or proprietary platform" choice
merely illustrate one of many negative aspects of this architecture.

One of NFS's biggest value propositions is its interoperability. To
quote some Wall Street guys, "NFS is like crack. It Just Works. We
love it."

Now, for the first time in NFS's history (AFAIK), the protocol is no
longer completely specified, completely known. No longer a "closed
loop." Private layout types mean that it is _highly_ unlikely that any
OS or appliance or implementation will be able to claim "full NFS
compatibility."

And when the proprietary portion of the spec involves something as basic
as accessing one's own data, I consider that a fundamental flaw. NFS is
no longer completely open.

Jeff