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Yes, I think that is correct. We are probably having this difficulty because
of a lack of a consistent definition of the term "distributed file system."
Here is the configuration I'm referring to:
______________
[LVS RS 1]-------------> | NAS |
| Server |
[LVS RS 2]------------> | |
| (NFS Server) |
[LVS RS 3]------------> |_____________|
Each LVS RS has /var, /usr, etc. on a local disk drive, but shared data is
placed on the NFS-mounted file system. (They are just ordinary NFS clients
to the NAS box). Lock arbitration is performed by the NAS box.
I think the terms "distributed file system" and "cluster file system" suffer
from the same problem of vagueness of definition. Awhile back Alan Cox had
this to say about the term cluster file system (CFS):
"It seems to mean about three different things
1. "A clusterwide view of the file store implemented by any unspecified
means" - ie an application view point.
2. "A filesystem which supports operation of a cluster"
3. "A filesystem with multiple systems accessing a single shared
file system on shared storage"
Meaning #3 can be really confusing because a 'cluster file system' in that
sense is actually exactly what you don't want for many cluster setups,
especially those with little active shared storage'
[For example if you are doing database failover you can do I/O fencing
and mount/umount of a more normal fs]"
--Karl
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