Coda File System

Re: Q: Is Partial Replication Possible?

From: Brian White <>
Date: Wed, 26 Feb 2003 13:02:18 -0500
> >Can CODA handle "partial replication"?  That is, can it handle having files
> >replicated across only some servers or does it always have to replicate
> >all files across all servers?
> The basic unit for replication in CODA is the volume.  You assign a
> volume to a "server group".  This server group may be any subset
> of CODA servers you have in operation.  (Well, it can't be the
> empty subset :)   So by this definition, CODA does handle "partial
> replication".

But each file within that volume is replicated ta all servers in that
group, right?

> >Let's say I have a system with 100 servers, each serving up files from a
> >large not-heavily-used archive to a local cluster of machines.  I have
> >these servers in place already for other purposes; using CODA to make
> >the archive available is just one more benefit.
> CODA does not serve data from other file systems.  Data in a CODA
> server must be stored in CODA via coda.  NFS can export an existing
> file system.  CODA can not do this.

I know what you're saying and I understand.  I was thinking of a "volume"
as a filesystem that is "served" by the various servers to all of the
clients.  The volume I was referring to was for this example the "large
not-heavily-used archive".

> >I'd like to be able to say that the files in this archive must exist on
> >at least 3 (for example) servers at any one time, but can be held on more
> >if it is convenient.  Such a setting would allow me to make use of the disk
> >space available across all servers (much like a raid) without each server
> >having to replicate everything.  Frequently used files would obviously
> >get replicated across many servers (for speed) while infrequently used
> >files would just reside in the minimum number of places.
> Server groups are not dynamic.  When you create a volume, it is assigned
> to a server group and that group of servers stores that volume and
> all files in the volume.  The number of servers storing that volume
> does not change.

Understood.  I guess the next question would be if there are any thoughts
about providing this feature?  It seems to me that this would provide the
benefits of a replicating file system along with the benefits of a raid.
The total volume size would scale automatically as more servers were added
to it.

                                 ( )

            On the road to success, you can be sure of one thing...
                   there is never a crowd on the extra mile.
Received on 2003-02-26 13:08:39