[Linux-cluster] Samba Technical thread

[David Teigland]

On Mon, Dec 06, 2004 at 11:56:21PM -0600, Christopher R. Hertel wrote:
> There's a thread started on the Samba-Technical mailing list that has some 
> discussion regarding cluster filesystems.  I'm learning fast, but I'm not 
> the right one to answer this:
> 
>   http://lists.samba.org/archive/samba-technical/2004-December/038326.html
> 
> An excerpt:
> 
>   The other network-like filesystems - Lustre, SANFS, GPFS, and RedHat's 
>   GFS do differ a little..  They differ in that they would attempt
>   stricter posix semantics and therefore view themselves as "cluster"  
>   rather than "network" filesystems (an odd distinction ... why shouldn't
>   a network filesystem simply consider "cluster" in effect a mount option
>   which would optimize for higher performance to nearby hosts in the
>   cluster and stricter POSIX file semantics rather than relaxed "nfs file
>   semantics").  If they had a good standards story with the IETF and were
>   inkernel in 2.6, perhaps no one would care, but it seems odd - when you
>   can make AFS or CIFS or NFSv4 do the same with rather more trivial
>   changes.
> 
> Somehow I think that the above doesn't quite capture what GFS is all 
> about.  I'm not trying to start a flamewar, but I'd certainly like to see 
> someone provide a clearer explanation than I could do.

There seem to be at least three different things there that can be
considered separately:

1. SAN usage
   CIFS/NFS aren't interested in exploiting SAN access from clients
   while others like GFS are.

2. server role (symmetric vs asymmetric)
   GFS aims to be server-less, NFS/CIFS are very server-based, and
   others can fall somewhere in between.  (If you consider using GFS
   above iscsi or nbd then the differences become even more subtle.)

3. POSIX semantics
   GFS semantics aim to copy those of a local fs exactly, while others
   like NFS don't, although there's nothing precluding that (NFS4 can
   be close if not exact).

-- 
Dave Teigland  <teigland at redhat.com>