Using Windows Server Failover Clustering with SQL Server: Are You Clusterphobic?

What do people fear most? Well the National Institute of Mental Health (NIMH) has compiled a list of the 10 most common phobias. Like all phobias, those on the list involve the environment, animals, or specific situations. Take a look:

1. Acrophobia – The fear of heights

2. Claustrophobia – The fear of enclosed spaces

3. Nyctophobia – The fear of dark

4. Ophidiophobia – The fear of snakes

5. Arachnophobia – The fear of spiders

6. Trypanophobia – The fear of injections

7. Astraphobia – The fear of thunder and lightening

8. Nosophobia – The fear of having a disease

9. Mysophobia – The fear of germs or dirt

10. Triskaidekaphobia – The fear of the number 13

It’s a good list, but I’m adding another one: clusterphobia. Clusterphobia falls under the category of a specific-situations phobia—the fear of using Windows Server Failover Clustering (WSFC) with SQL Server. There are a number of reasons why you may be developing or have clusterphobia:

1. Windows Server Failover Clustering (WSFC) is expensive and too hard to build/set up

Rigid rules – While the rules regarding having to use the exact same hardware configuration for every server in the cluster have relaxed somewhat, WSFC still has very specific configuration rules that can make building a cluster a real head-scratcher.

Low utilization – The easiest cluster to set up and manage is a passive/active configuration. Only one server is actively hosting SQL Server, while the other is idle. This effectively cuts your utilization in half.

Highest software cost (OS and SQL) – Because of the way Microsoft has constructed its licensing terms, using WSFC and SQL Server to support a cluster larger than 2-nodes with maximum flexibility to reassign licenses more than once every 90-days during failover requires customers to purchase Enterprise Edition, plus Software Assurance.

2. WSFC is a poor consolidation platform

The more SQL Server instances and servers you put in a single cluster, the more complex it gets to manage—which in turn makes it more likely to break. This dynamic makes using WSFC for high levels of consolidation risky and encourages the use of multiple 2-node passive/active clusters which is the antithesis of a consolidation platform.

3. WSFC and virtualization double the complexity

Using virtual machines (VMs) with SQL Server is a great platform. But when you layer this platform on top of WSFC, problem isolation and root cause analysis become very difficult. If there’s an issue, is it with the underlying VM host server, the VM, WSFC, SQL Server or some combination thereof? Solving the problem requires strong effective cooperation and communication across IT teams.

How Do You Overcome Clusterphobia?

Like all phobias, clusterphobia is a treatable condition. It can be overcome with cognitive and behavioral therapy techniques. Specifically, I encourage the following steps:

1. Acknowledge that clustering as a general technique to increase the availability of applications and services is not bad. There are only bad clustering products. Clustering has been around and used in various forms since the ‘60s. Research your options to avoid anxiety-producing choices and you’ll be in much better shape.

2. Remember that clustering does not equal Microsoft WSFC. Be willing to move beyond Microsoft as a solution provider for your SQL Server clustering needs. There are a number of companies (e.g., VMware, DH2i, Citrix) that offer alternative solutions for making SQL Server highly available and disaster tolerant with better flexibility, features and lower costs.

Regarding the NIMH list above, what’s your #1 phobia?

Related: Identifying SQL Server Failover Cluster Share Drives, Nodes, and Current Ownership