Re: NFS as a Cluster File System.

[Alan Robertson <alanr@unix.sh>]

Lorn Kay wrote:
> 
> Is NFS a viable CFS? (I'm cross posting this due to a discussion on the 
> the linux-ha list recently.)
> 
> NFS has a bad reputation probably due to (at least) the following:
> 
>     It has been used in networking environments where different server 
> hardware configurations (NICS, drivers, etc.) running different 
> operating systems have connected to each other (in many-to-many 
> configurations).
> 
>     It “grew up” on networks that were perhaps unstable, or immature 
> (“Someone’s kicked the token ring coax cable laying on the floor again”) 
> long before switches were common place, and the network was loaded down 
> with all kinds of network traffic.
> 
>     It wasn’t understood very well. Since the default mount options 
> worked, system administrators often didn’t fully understand the 
> ramifications of their NFS client mount option choices.
> 
>     It relied on UDP, which is susceptible to huge retransmission 
> efforts on noisy or lossy networks.
> 
>     NFS was used over many-hop WAN connections.
> 
>     NFS servers were often used for many other tasks, not just NFS.
> 
> 
> A cluster configuration, however, offers several advantages over the 
> typical NFS configuration:
> 
>     All NFS clients (the cluster nodes) run the same operating system 
> (Linux).
> 
>     All clients run the same version of NFS and the kernel.
> 
>     All clients use the same network tuned configuration.
> 
>     A physical network can be dedicated to NFS. (Using a high quality 
> switch, with short data-center-only cable runs.)
> 
>     All clients connect to one NFS server.
> 
>     The NFS server is a high-quality dedicated machine (Net App, EMC, etc.)
> 
>     Only one mount point need be used with one set of mount options.
> 
>     Linux clients can use TCP instead of UDP.
> 
> Except for the vagaries of the load placed on the cluster nodes, this 
> sounds like a test lab environment. If NFS can’t work in this 
> environment where will it ever work?

NFS V3 and before have problems with "cache coherency".  That is, the 
different nodes in the cluster are not guaranteed to see the same contents.

I think this is supposed to be fixed in v4.


-- 
     Alan Robertson <alanr@unix.sh>

"Openness is the foundation and preservative of friendship....  Let me claim 
from you at all times your undisguised opinions." - William Wilberforce




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