Highly available and scalable Cyrus configurations

[Rob Siemborski]

On Tue, 7 Oct 2003, Ben Carter wrote:

> and an MTA on each cluster member, because with the murder
> configuration, you probably have to end up with a load-balancing switch
> in front of murder front-end machines which in turn are in front of the

This is not the case.  Simple DNS round-robining is sufficient.

> design, backend machines would have to be clustered anyway (2-node
> clusters probably) to eliminate the back-end machines as SPOFs.

Well, the aggregator isn't solving the HA problem.  It is doing its best
to mitigate it however (via partial failure modes).

> And my second question is: is there something I'm missing with regard to
> the Veritas cluster being a much simpler configuration to troubleshoot
> and operate and a much stronger configuration in terms of availability?

Well its simpler unless it breaks or has poor performance.

I'm not familiar with the Veritas cluster (we have had good experience
with vxfs on our backends however).  You also probably want to be sure
you're not replaceing one single point of failure (a backend) with another
(the cluster).

The key about the usability of the filesystem is that file locks need to
be obeyed throughout the entire cluster, and mmap() needs to be efficient
(and able to deal with read()  and write() being called on that file at
the same time).

Also, the murder does get you one performance advantage that the veritas
cluster (even correctly implemented) does not: it provides a large number
of read-only copies of the mailbox list that clients can use for LIST
operations, and not interfere with updates of the master copy.  With the
size of mailbox lists on systems that are considering HA options, or
moving to an aggregator configuration, this is, in fact, a serious concern
to think about.

-Rob

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Rob Siemborski * Andrew Systems Group * Cyert Hall 207 * 412-268-7456
Research Systems Programmer * /usr/contributed Gatekeeper