Most large organizations using exchange want some type of “high availablity.” This often leads to requests or inquires about a cluster setup. There are many different ways to setup a cluster and we will explain the basics. For the purpose of this post, we will simply refer to setup of a cluster running Microsoft Exchange.

Microsoft natively supports clustering with Windows Server 2003 Enterprise Edition and higher. The standard edition will not work. This setup is expensive because it requires at least 2 servers running EE (enterprise edition) and also a NAS or SAN to store the exchange data. Mail cannot be stored on one or more servers as all servers in the cluster will need read/write access to the data. Once those bases are covered a cluster can be setup one of two ways:

• Active-Active
• Active-Passive

Active-Active means both servers are operating all the time. This is primarly used when 1 server cannot carry the load by itself. If one server fails in this type of setup, performance decreases dramatically and problems start immediately.

Active-Passive mean one server operates and if that server fails, the other takes over. This is a more common approach many organizations. This is fairly easy to setup and recovery time can take as little as 30 seconds.

Besides traditional clustering, there are a few 3rd party applications that will work as well. These applications DO NOT require the use of EE or a shared storage device. However, they are very expensive and can be tricky to install. Double Take Software is very flexible as it works with various types of software (Exchange, SQL, and Sharepoint) and also works well with VMware. Double Take can also work as a tool for migrations or other situations where a 1 server may need to go offline for hardware or software maintenance.

The second product is called NeverFail. This product also targets Exchange, SQL, and Sharepoint. Both software packages have outragous price tags, but for organzaztions looking for this type of solution, you have to pay to play.

The two 3rd party packages mentioned here both work and they work well. They are very similar products but have very diferent menthods for doing what they do. If you are in the market for a cluster contact us. We have worked with all three solutions and can point you in the right direction based on your existing setup and budget.