Coda File System

Re: Thinking of Coda

From: Jan Harkes <>
Date: Sat, 9 Feb 2002 13:35:05 -0500
On Sat, Feb 09, 2002 at 12:25:50PM -0500, Yan Seiner wrote:
> I have two offices joined by a wan.  Currently we are mirroring files
> between the offices using unison, but that is not working very well.
> We need a more robust solution.
> We are getting more bandwith - a minimum of 128Kbit/sec; possibly as
> high as 640Kbit/sec SDSL.
> We sync typically about 100MB / day with several hundred files.

> a) coda can work with this limited bandwith

This seems to be a pretty common scenario, however. Coda's server
replication is quite bandwidth intensive, i.e. when resolving conflicts
files are being fetched to one server and then redistributed.

Furthermore, clients need to check the attributes of objects on all
servers in a replicated group as it is the clients that detect the
actual version differences and trigger the resolution.

So using Coda for it's replication won't work in this situation. You
could use Coda servers on both sites that are not replicating a volume
between each other. So the volumes of 'local' users would be stored on
the 'local' server. The problems here are, which site hosts the
'root-volume' of the /coda tree located as the remote site will suffer
from the low bandwidth link, and although large client caches can
eliminate some of the data fetches across the link, it's each client
for itself, so even with only minimal sharing the amount of cross-site
traffic is still considerable as it's N clients * M amount of shared

> b) coda is stable enough to use in production

It depends, my typical answer would be no, there are still known bugs
and problems that are pretty hard to solve. Administratively it is not
an easy system to set up and maintain, and the optimistic replication
sometimes presents users with conflicts they don't want to deal with
especially when there is a deadline.

But for a small setup with only a few servers, users that are adaptive
enough to work from the local disk while a problem is being resolved and
an knowledgable administrator it can work reasonably well.

i.e. It works here at CMU 24x7 with 6 servers, and about 25 users
(typically 5-10 active clients during the day, so I'm guessing only
about 5 active users that use Coda as their main means of keeping their
data with them when counting both their desktops and laptops)

Received on 2002-02-09 13:35:07