For many organizations, the major motivation for implementing virtualization is reducing data center cost. It all sounds so easy: Reducing the amount of physical servers must provide a cost benefit, right? That's what you might think when talking with a sales person who is trying to sell you on virtualization; however, there are additional expenses that come with virtualization which aren't as apparent as the money saved on hardware. Today we'll examine some of these virtualization cost factors.
High availability costs with virtualization
When implementing virtualization, you probably want to minimize the impact of a physical machine crash. If a physical machine hosting four virtual machines goes down, the impact is enormous and that's why a virtualized environment always comes together with additional investments on the network. To make it as redundant as possible, you'll need to put the virtual machines themselves on the Storage Area Network (SAN) and it will help to have a high availability (HA) option that protects your virtual machines if one of the physical machines goes down.
Nowadays, most organizations already have a SAN in place, so chances are that you don't need to make an additional investment in that; but the high availability solution will cost you extra in most cases, primarily for two reasons. First, in order to make sure that HA works smoothly, you need a fencing mechanism that terminates failing physical nodes. This is required to make sure that a situation where a virtual machine gets started at two physical servers at the same time can never happen. Such a situation is real because, without fencing, network infrastructure problems would run the risk of a split brain in which both halves of the cluster think the other half is down. Therefore, fencing is necessary and, since fencing is hardware based, it will cost you extra.
Licensing is a second factor affecting HA implementation costs. All of the major virtualization platforms charge extra for high availability and these can be quite high. Only the open source virtualization platform Xen offers a free HA solution, available in the form of Heartbeat clustering; but this solution is so complex that only few seem to master it completely.
Additional costs of virtualization
Another major cost factor when implementing virtualization is in administrative costs. In big organizations, virtualization projects tend to become very complex, so you'll need some people who are devoted to them. Even in small organizations, your people need to be skilled in order to manage the added complexity in a virtualized environment. Expensive training courses and the extra work can easily add up to tens of thousands of dollars on a yearly basis even for small organizations. For the same amount of money, an organization can install a couple of additional physical servers.
Since virtualization adds to the complexity of your IT infrastructure, this becomes another source of increased costs. For instance, an old backup system might not be versatile enough to back up either file systems or complete virtual machines and may require additional licensing. And don't forget that a decent management interface doesn't come cheap, either. The best you'll get for free is a graphical or web based management interface that allows you to manage one server at a time.
Finally, the fact that your servers are used more efficiently in a virtualized environment means that they will consume more power as well. The power supply that was installed for your rack may do well for a server that has a load average that doesn't go beyond 20%, but once all your physical servers get an average 70% workload, they demand more power and that may mean upgrades to the power infrastructure of the datacenter. If this includes the uninterruptible power supply (UPS), the expenses necessary to implement virtualization in your data center will increase even more.
Implementing a virtualized environment may initially look like something that helps reduces data center costs; however, training, additional licenses and infrastructural measures come with their own price tags. When making cost calculations for virtualization, make sure to consider all of these, which will help prevent unwanted surprises on the expense side.
About the author: Sander van Vugt is an author and independent technical trainer, specializing in Linux since 1994. Vugt is also a technical consultant for high availability (HA) clustering and performance optimization, as well as an expert on SUSE Linux Enterprise Desktop 10 (SLED 10) administration.