Sunday, December 5, 2010

When do we need a Failover Cluster solution ?

An interesting question was raised in the forum this weekend. “When is it overkill with Failover Cluster?”
We should think of failover clustering as a solution, and not a product. We have to examine our needs, pros and cons, and the cost. My reply to this thread can be red in its entirety here:

You ask a very interesting question: “When is it overkill with Failover Clustering”
It is tempting to say: never, but as with many other aspects in the IT infrastructure,- it depends.

It seems to me that you already have the hardware/software required for running Failover Clustering.
And since you are also running 2008 R2, you have the ability to enable CSV, and later support dynamic memory with the release of Service Pack 1.

Are you considering an Active-Active cluster, or Actice-Passive cluster? To get the most out of your HW, it`s recommended to use active-active, and as mentioned earlier, with SP1 this will allow you to over commit your hosts and ‘decrease’ the requirements for additional HW.

When it comes to administration and management overhead of the cluster, you really have to look at the benefits to be able to weigh that against each other.
It gives you redundance, easier maintenance on your physical nodes in the cluster, simplified administration of your VMs, and much more.   In addition, you can also create guest clusters within the VMs, for your SQL server etc. The key word here is ‘highly available’.

As you may know, Failover Clustering requires an Active Directory domain. It is recommended to place this role outside your cluster. I have written some posts about this topic on my blog, check it out here: and here:

Since you are planning to have another pair of blade servers and SAN at another physical location, you should also consider Multi-Site clustering, that will extend the cluster from being only Highly Available but also a Disaster recovery solution. Check it out here:

To answer your question, it really depends on your needs. In comparison, we are 50 employees in our company, and we`re running Failover Clustering with 4 nodes at our primary location, and have a disaster recovery site as well. We develop and deliver software, services, and need to be available to our customers  24/7. We`re also running some services in the ‘public cloud’ that is synced with our servers on-premise.

Technically you have the foundation for a Failover Clustering solution, but you should examine your needs. 

No comments: