How many administrators believe today that applications such as Microsoft Exchange, Citrix and Microsoft SQL are not good virtualization candidates?
More times than not, administrators that are reluctant to virtualize applications like these usually centralized their server infrastructure and are supporting large user bases accessing a load-balanced solution or a multi-node cluster. Thousands of mailboxes, hundreds of simultaneous sessions or concurrent job processing does not sound like a good fit for virtual machines at first glance, especially if you are only focused on migrating the current physical clustered configuration as is. Although possible to recreate as virtual machines, it is usually more complicated and therefore not desirable to attempt to P2V these configurations.
My opinion on this topic is that the advantages of virtual infrastructure sometimes warrant a redesign of the clustered service. In other words, consider changing the clustered design back into multiple stand alone virtual servers in order to leverage the unique virtualization features like live VM migration, distributed resource pooling, snapshots, and VM mobility. Let the virtualization hosts become the multiple nodes of your centralized model. If centralized user administration is the primary concern, then even though split into several VMs, all of your users, services and data are still under one roof, protected by the same UPS, and local to the same backup solution.
What about the potential for additional savings and efficiencies? We already know VI reduces power consumption, heat output, and takes up less rack space. You can go back to a Windows Standard version instead of an Enterprise or Data center edition. By eliminating the need for dedicated private heartbeat networks between the nodes you can reduce cabling and network ports. Administrative burden is reduced by doing away with cluster service accounts and specialized user and group permissions. Storage requirement complexity is minimized.
Finally, if concern for performance is the main barrier then consider the following. Even if you had a 1:1 consolidation ratio with an Exchange, SQL, or Citrix VM isolated on its own virtual host so it has exclusive access to physical resources, you still achieve most of the virtualization benefits discussed already.
The baselinemag.com article Virtualization Is the New Clustering by David Strom explores many of my points in greater detail and summarizes my opinions with the following quote:
“The combination of better resource use, reduced power and cooling in the data center, and more manageable applications delivery has made virtualization a very popular solution. As IT shops gain more expertise in delivering virtualized applications, they can also get a better handle on the kinds of load balancing and availability issues that once were the exclusive domain of clustering solutions.
“Indeed, virtualization continues to be complementary to—and is sometimes a less expensive replacement for—some applications that don’t require the up-to-the-nanosecond transaction-level failover that clustering provides. “