Hi all,
My client is a relatively small business - instead of racks full of blades,
we're talking about a handful of servers in a single site. So you guy who
are used to implementing a 16-node Exchange cluster with a SAN the size of a
boxcar need to scale down your thinking to follow this scenario.
My client uses a SCC-type cluster under Exchange 2003, and hosts some other
low-impact clustered virtual servers such as file shares for business records
(Word and Excel docs) on the same cluster. Given the amount of mailbox
traffic Exchange is loafing, so it's no problem to put a few other things on
the same cluster. Normally a small business like this might not use a
cluster, but my client likes the extra reliability and automatic failover.
Now we're looking at buying a new server and upgrading to Exchange 2007
within the next year. With Exchange 2007, Microsoft seems to recommend CCR
over SCC as a better high availability choice because of the two complete
copies of the database, and because you can save money by skipping the shared
storage (SCSI in my case).
However, my client likes the redunancy of a cluster for his business data as
well as for Exchange, so he wants a new cluster with shared storage. The
Microsoft Cluster folks recommend that you stay away from a MNS cluster if
you can because there's less chance of "losing the quorum". The Exchange
folks don't necessarily disagree but have offered the MNS option to reduce
costs and allow for geo clusters.
With this background, I wondered if I can create a standard (not MNS)
Windows cluster server, put the business data shares on shared storage, and
then install Exchange in a CCR configuration instead of a SCC configuration.
It would put more disks on each node and less shared storage, but for better
reliability that's a small price to pay. Besides, the per-node SAS drives
are cheaper than the shared Ultra Scsi drives.
The Exchange documentation assumes that the SCC configuration will be used
with a standard cluster, and the CCR configuration will be used with a MNS
cluster. However I couldn't find any statement either way about whether an
CCR configuration will work on a standard cluster, and I certainly couldn't
find a statement that it's not a supported configuration.
So I tried it. It turns out that when you try to install Exchange in CCR
mode, setup complains because it doesn't see the Majority Node Set resource.
However, it's easy to add a File Share Majority Node Set resource to your
existing quorum group; since the cluster is not a MNS cluster Windows ignores
the resource, but it has no problem if you create it.
With a dummy MNS resource in the cluster to bypass the overly simplistic
Exchange setup prerequisites check, the actual install worked fine and CCR
started working flawlessly. Failover and failback work, both from within the
Exchange Management console and from the Cluster Administrator. Nothing
funny in the event logs. Also, the Exchange Best Practices Analyzer said
everything was A-OK.
So, if you find yourself with similar requirements, I'm here to tell you
that all you need to do to get Exchange to install in CCR mode is to create a
dummy MNS resource. You can probably delete it afterwords but I intend to
leave it so I can install future service packs.
Also, if anybody from the Exchange product team is reading, please fix your
prerequisite checker to allow installation of a CCR mailbox store on any
working cluster (you don't need any shared storage, so what do you care what
kind of cluster it is)?
Finally, if anybody sees any strong reason to stay away from this scenario
please let me know. I could alway set up Exchange in SCC mode instead but I
haven't seen anything that says what I'm trying to do is unsupported so why
not get the benefits of CCR?
Regards,
Mike Gilbert