Today I saw an article over at ComputerWorld that talks about Virtualization's downsides. It brings out some interesting points, but I think you can easily overcome them. Here are my comments on some of the points they criticize.
(Since I am more familiar with Virtual Server than with competing products, I will concentrate on Virtual Server’s features)
- Increased uptime requirements: This is something that has been on my mind since I started working with Virtual Server. Recently I had the change to setup a Virtual Server host cluster, and I think that is the way to go to minimize this concern. With Windows’ clustering capabilities, you can take out a node in the cluster, and another node will continue running the virtual machines. The virtual machines will only be unavailable for a few seconds while the resource group changes from one node to the other.
- Bandwith problems: One of the recommended scenarios for running Virtual Server is to remove everything from a NIC on the host server except for the virtualization driver. You can extend this recommendation, and use several NICs on the host, each NIC associated with just one VM. Still, if you have something like a very high-traffic website, you’ll probably be better of running it on a physical server instead.
- Cost accounting - license compliance: Microsoft has released new licenses for their server products that make them virtualization-friendly. You can review it here, and see how many licenses you need for your planned configuration. Licenses for other application may be messy, though.
- Vendor support: This is something that the industry will have to sort out. Something similar happened with the move to multi-core systems. Some vendors treated dual-core CPUs as two processors (thus requiring two licenses), while other adapted a “per-socket” approach. Other even adapted even stranger policies (dual-core = 1.75 licenses ???). Again, the market will have to adapt to the new virtualization paradigm.
- Management Complexity: Managing virtual machines as opposed to physical machines is definitely more complex – you basically have to perform all the management tasks that you normally do for physical boxes, PLUS the overhead of managing virtual machines. Management tools are still in their infancy, but with the eventual release of
CarmineSystem Center Virtual Machine Manager plus a fully WMI-based API, the management effort should be reduced significantly.
Then again, there are some workloads that don’t work well when virtualized. Database servers are a classical example of this – IMHO it is a better idea to have one large database server and hosts several database in that SQL Server instance (for example), than to have several virtual machines each one with a separate SQL Server instance hosting different databases.