 What
to Do When the Server Doesn't Serve -- Using CODA
Brett Lymn
In the previous articles in this series, I looked at NFS failover
methods using fairly mainstream free software and the operating
system facilities themselves. In some environments, this is probably
a good fit for providing some measure of redundancy in your file
servers. This time, I shall look at another approach to providing
access to files by using a file system called CODA that is specifically
designed to handle server outages.
CODA
CODA is an intriguing file system being developed by a group headed
by M. Satyanarayanan at Carnegie Mellon University (More information
on CODA can be found at http://coda.cs.cmu.edu/.) This file
system has been designed to be able to operate when the client has
been disconnected from the server without disrupting normal operations.
The CODA file system is an experimental file system. The decision
to use it in a production environment must be weighed very carefully,
because glitches in the software may result in CODA eating your
file system and causing loss of data. Having said this, the actual
situation is somewhat better; CODA does work. It is not very forgiving
in some circumstances, but if CODA is treated reasonably in terms
of system resources, it works well. A major advantage of using CODA
as a failover file system is that it is, by design, able to gracefully
cope with network outages.
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