[Lustre-discuss] NFS vs Lustre

[Nicolas Williams]

On Sun, Aug 30, 2009 at 08:16:52PM -0400, Brian J. Murrell wrote:
> On Sun, 2009-08-30 at 16:12 -0500, Nicolas Williams wrote:
> > One thing about NFS is that it's meant to be neutral w.r.t. the type of
> > filesystem it shares.  So NFSv4, for example, has features for dealing
> > with filesystems that don't have a notion of persistent inode number.
> > Whereas Lustre has its own on-disk format and therefore can't be used to
> > share just any type of filesystem.
> 
> You have "stumbled on to" an interesting, significant difference between
> NFS and Lustre.  NFS is a protocol for sharing an existing filesystem.
> Lustre is a filesystem -- so much so in fact, that NFS can even share it
> out.

Indeed.  pNFS is not really a protocol for sharing generic, pre-existing
filesystems anymore either.  The moment you want to distribute the
filesystem itself you can no longer just substitute any filesystem into
an implementation of the protocol.

(Yes, I understand that when Lustre was layered above the VFS one could
conceivably have changed the underlying fs, though that didn't work out,
if for practical reasons.  But even then, one couldn't have used the
underlying fs directly, not in a meaningful way.)

Nico
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