Hi Brain,

>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".


>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'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.

I hope this helps.

--Phil
 

-- 
Phil Nelson                       NetBSD: http://www.netbsd.org
e-mail: phil@cs.wwu.edu           Coda: http://www.coda.cs.cmu.edu
http://cs.wwu.edu/faculty/nelson