Re: Re: NFS as a Cluster File System.

[Donavan Pantke <avatar@dcr.net>]

On Thursday 09 January 2003 18:13, Lorn Kay wrote:

>
> Sorry, still confused about what a "CFS" really is. In "In Search Of
> Clusters" Gregory Pfister takes the position that a distributed file sy=
stem
> is what he calls a valid "single system image" file system, what I woul=
d
> take to mean a cluster file system (though he doesn't use those words).
>
> I guess you are saying a clustered file system isn't necessarily suppor=
ting
> a cluster of application servers but is itself stored on a cluster. (A
> single server can be the only server using a cluster file system.) ?
>

=09Typically, the term CFS refers to a set of servers that work on the sa=
me=20
storage at the same time. What this means is that my central storage syst=
em=20
could have multiple servers mounting a file system at the same time.=20
Currently, preforming this is still in development; the difficulty is tha=
t=20
all nodes have to tell each other in some way about exactly what they're=20
doing to keep from corrupting the data on storage. Until this matures for=
=20
production use (It's my presonal opinion that there are still too many bu=
gs=20
in current implementations), the next best answer is for a highly availab=
le=20
cluster of servers that handle data requests. This is where NFS comes in.=
=20
Although I agree that in some applications this isn't workable with NFS, =
I've=20
found it to be quite a boon. At my workplace, we have a great many machin=
es=20
accessing common data. We started with a M$ cluster using SMB, but the na=
ture=20
of the protocol means that when the cluster fails, each client can't acce=
ss=20
currently open files. they have to close and re-open each handle. The=20
stateless nature of NFSv3 and v2 is stateless. This means that a cluster =
can=20
fail over and clients simply pause requests untile the filesystem is=20
accessible again. Not a good soution for applications with very high resp=
onse=20
time requirements, but it works for us. BTW: When describing clusters her=
e=20
I'm referring to a active-passive pair of servers where resources move wh=
en a=20
failure has been detected.

=09Donavan Pantke


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