Virtualization is among the hottest trends of recent years in both desktop and enterprise computing, and for good reason. Virtualized platforms not only maximize hardware utilization and efficiency, but also allow for robust, secure, centrally managed deployments of operating systems and software for testing and production environments.
There are now many virtualization products on the market, offering server virtualization, desktop virtualization, and even application virtualization. While every product has its own particular advantages and limitations, consider these tips when devising your virtualization strategy.
Enable virtualization in BIOS.
This may seem like a minor point, but it should not be overlooked. Modern processors include built-in support for virtualization that can be either helpful or mandatory for certain software virtualization platforms. In many machines, VT support in the BIOS is enabled by default — but not always. For some brands and models, you may need to enable VT through the machine's BIOS menu. Instructions for configuring your BIOS will vary by model. At the very least, don't simply assume that the hardware you plan to use as a virtualization host has hardware VT support enabled; check it yourself.
Optimize your virtual machines-per-core ratio.
One of the great values of virtualization is running multiple virtual machines (VMs) at the same time. Because each VM can be designed for a particular kind of purpose (for example, one VM might be a Linux mail server and another could be a Windows Web host), you can maximize utilization of available CPU time. But how many VMs should you run?
Today's processors offer multiple cores, with each core effectively behaving as an independent CPU. Virtualization vendors provide a spec for the maximum numbers of VMs per core supported by their product, but in practice, most installations will deploy far fewer VMs per core than the maximum limit.
There is no one-size-fits-all answer to your ideal VM-per-core ratio, but the industry rule of thumb for typical deployments is three to six VMs per core. One significant variable to consider is how much memory is available. To optimize your VM-per-core ratio, be sure that there is at least 4GB of physical RAM for each core (so a 4-core processor will need 16GB RAM). Monitor the memory needs of each VM, and adjust its memory allocated to fit, so that it does not allocate excess physical memory.
Measured or observed response time is another method to calibrate your VM-per-core ratio. In other words, to the end user, each of your VMs should respond to requests with the same speed as if they were dedicated machines. When a VM is delayed responding to a request, that means the physical host machine has insufficient resources for all of the VMs running, and that you either need better hardware or fewer VMs.
Use physical storage for high-I/O applications.
Most virtualization products allow you to configure either virtual or physical storage for a guest VM. Virtual storage takes the form of one or more files stored on the physical hard drive, where the file emulates a "real" hard drive. The VM reads and writes to this file, although the platform "thinks" it is reading and writing directly to physical media. Virtual storage is convenient because it is easy to copy, back up, restore, and migrate between physical media. But accessing it can be slow, especially for I/O-intensive applications.
For example, a virtual machine that is running a SQL database server with a high load is a poor candidate for virtual storage. In this case, you will significantly improve performance configuring the VM to read and write directly to a physical hard drive.
Enjoy elastic virtualization capacity using Amazon EC2.
If you haven't had occasion to meet Amazon EC2, it is a consumption-based cloud service. Essentially you can rent space and processing time from the EC2 data center, paying only for what you use. EC2 is a good solution when your data center needs fluctuate, because you don't need to invest in your own hardware capable of handling variable high-load scenarios. Although you can use EC2 simply for file storage and data backup, you can also use it to run virtual machines. Many pre-built virtual machines are available in Amazon's native AMI (Amazon Machine Image) format, or you can import VMWare-created virtual machines. Running a VM on EC2 means that it will have as much processor capacity and memory allocation as it needs for the current demand being placed on it.
For more information, see:
Protecting Users With Virtualization
Making Virtualization and Compliance Work Together
Desktop Virtualization Tries to Find Its Place in the Enterprise
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