The first thing to do is work with your customers on guest placement on their hosts. I've seen both overzealous and overly timid administrators working with virtual environments. The overzealous want to have as many guests per host as possible and don't think about the impact to the application users. Overly timid administrators give more resources than necessary to a guest and put the least amount of guests on a host. Giving more resources than necessary leaves a significant amount of unused resources on the server, even though the resources are allocated to a VM they're not being used and could be re-allocated to another virtual machine.
The whole point of virtualization is to do more with less while providing the same end user experience. The overzealous solutions provider causes tension among customers because application owners will have had better performance prior to virtualization. A timid solutions provider causes tension because the business owners are paying more than they have to for their virtual machines.
Using tools to achieve optimal vSphere performance
VMware's Distributed Resource Scheduler (DRS) aids both types of solutions providers with their respective scenarios. In vSphere 4, DRS allocates resources to guest systems based on a weighted system that gives more resources to the guest with the higher priority. DRS also uses the current condition of each host in the cluster of a new guest system to determine the best guest placement. Make sure you educate your customers on the benefits of DRS and how to use it after you've finished the project.
When you create a guest system and place it on the host, make sure that the latest version of VMware Tools is installed and that all unneeded devices are turned off. By turning off unneeded devices, you'll free up additional resources on the hosts and guests and help mitigate some potential security threats. Some examples of unneeded virtual devices include CDROM, floppy drivers, USB and sound.
Once the guest system is placed on a host system, the next step is to establish a connection. With VMware, you can use VMware Virtual Machine Remote Control (VMRC) to connect to the virtual machine, but VMRC was always meant to be more of a virtual KVM then a connectivity method for end users and administrators. Using VMRC also creates some overhead on the hosts with each connection. To keep the overhead to a minimum, use built-in tools, such as Microsoft Remote Desktop Protocol, Secure Shell or Telnet.
Outside activities influence vSphere performance
Activities that are happening in the guest operating system can also have an impact on the hosts and the cluster. Antivirus and backups can have a significant influence on the entire virtualization stack. Let's say there are 40 guests on a host and 10 hosts in a cluster. If the antivirus software runs at noon, 400 systems will be running a disk-intensive routine at the same time on shared resources. The same concept applies to backups. Be sure you consider these types of activities when implementing vSphere or any virtualization project. Turn off things like X Windows in Linux on each guest operating system that will be virtualized if it's not needed; enhanced visualization modes in Windows, such as Aero; and any screensavers or other graphics-intensive applications.
This is by no means the be all and end all of performance-tuning in a vSphere environment, but it is a great place to start when you're talking with your customers. The real key to performance tuning isn't just throwing newer, faster hardware at the problem -- that doesn't hurt, but it sometimes treats a symptom and not the real issue. The key to obtaining optimal performance of vSphere is in tracking guest and host performance and making smaller adjustments and tweaks to your environment over a long period of time.
About the expert
Jason Kappel is an infrastructure architect and virtualization expert at Avanade Inc. He specializes in enterprise infrastructure and data center optimization, virtualization and systems management. He has worked with some of the largest companies in the world to implement green data center solutions and has implemented several multinational server and desktop virtualization systems.
This was first published in September 2009