VMWare limitations

The new office uses VMWare's ESX infrastructure for the vast majority of their servers and there are a lot of cool features about the product. We have a fiber channel SAN at the data center and all four VMWare ESX host computers can view and see the same volumes. This allows you to move the VMs on the fly from host to host if one of the VMs needs more processor power or something. you can use the same trick, called VMotion, for maintenance. You can slide the VMs off of one host, patch and reboot, and the move them back without any downtime.

However, I am firmly convinced that there are a couple of limitations:

• Domain Controllers do not work well as virtual machines. All DCs should be actual servers.
• SQL 2000, SQL 2005, and other databases should only be run on actual servers.

The company a whole has also decided that all back-end Exchange servers should be actual servers instead of virtual ones. I haven't experimented with that to decide if I agree.

We have two Microsoft MOM 2005 database servers and a couple of other databases for web-apps, all of which are virtual servers. They have been nothing but trouble. We have been adjusting virtual CPU and RAM settings, changing the ESX host settings, and have been trying every trick that VMWare recommends to us and they all run like crap. At low loads, everything is fine but as soon as the SQL load increases, the performance gets very bad, very quickly.

So, save yourself some pain and make sure every DC and every database server is running on real hardware.