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Should I Consider a 100% Virtualized Environment?

Although you will find that having a 100% virtualized environment is certainly achievable, there are a few reasons why you might want to maintain a few physical servers:

  • Support issues. Some application vendors may require you to reproduce the problem on a physical server if they suspect the virtual host might be causing the problem. For this reason, it is a good idea to keep a physical server around for certain infrastructure components like Active Directory. If you have eight domain controllers in your environment, you might consider virtualizing six of them and leaving two of them as physical servers. Same with database servers; if you leave one or two Oracle or SQL database servers as physical servers, it gives you the flexibility to move a database hosted on a VM to a physical server if the vendor requests it.
  • Infrastructure issues. If your environment suffers a major failure (for example, a storage area network [SAN] goes down or you experience a major network failure), you may lose most of your VMs. For this reason, you may want to copy at least one DNS/DHCP physical server (because many functions rely on DNS to work properly).
  • All the eggs in one basket. You will most likely be using shared storage with your ESX hosts to take advantage of all the features that require it. However, if something happens to that storage, it will affect all your hosts and VMs that utilize it. To offset this risk, consider running a few of your key infrastructure VMs (for example, domain controllers, authentication servers, database servers, and DNS servers) on local disk rather than shared storage. That way the VM will not be affected if something happens to your shared storage device.
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