Distributed clustering plusses and minuses

In the new Server 2008 platform offering from Microsoft, another option for Failover Clustering (Multi-Site Clustering or MSC) has become available.  This is a great option for distributing a cluster amongst multiple, physical locations; but does have some limitations.  As it may be used as a platform for creating Exchange 2007 site redundancy, I'll go over some of the basic stuff here.

First and foremost, you're network will need to be ready to handle this kind of failover solution.  Since the subnet and latency limitations of 2003 clustering - for the most place - don't exist in 2008, this isn't as much of a barrier to entry as it used to be.  However, you will still need enough bandwidth to handle replication traffic, and you'll need to be able to support your end-user population when they need to work on the other side of link if the production node dies.  This is different than normal DR solution sets in that it is expected that you'll run off the secondary node at least some of the time during normal production operations, instead of only during an emergency.  So instead of preparing for only having a sub-set of users running on the other node, you'll have to be ready to have all your users running on it from time to time.

You're also going to need at least one more server in the equation to act as the File Share Witness.  FSW is a solution designed by Microsoft that can allow a cluster to arbitrate which nodes are allowed to take over if the nodes themselves suddenly can't see each other.  It's critical that the server that holds the FSW, therefore, can see both servers, and can see the correct server (the one you want to take over) in the event of a site failure.

On the subject of networking, you'll want to take a quick look at this KB article, which goes into some great tips for properly setting up DNS entries, etc:

http://support.microsoft.com/kb/947048/en-us

Now, once you have all this in place, using MSC for site redundancy is an incredible solution set.  With the right third-party tools, you can not only protect Exchange 2007 (which natively replicates via SCR), but SQL, File, IIS, and anything else that can use Server 2008 Clustering platforms. It provides both the standard cluster tool-set (now called Failover Clustering or Shared Copy Clustering), and new Network Load Balancing options in addition to the Multi-Site solutions.  For those familiar with clustering - or those who want to become familiar with it - this is a superb failover platform for any application is cluster aware.

While it's not for everyone, especially smaller IT shops that may not have Clustering expertise, MSC is a robust platform built on well-tested technologies.  It is not only a logical next-step for Microsoft, but a great way to integrate Clustering into your organization to provide for more than just single-site availability

LiveJournal Tags: Clustering Server 2008 Availability multi-site multi-subnet

.