How To Backup Virtual Servers

As server virtualisation assumes a greater role in the enterprise, administrators face a proliferation of virtual machines residing on the same physical server. Each virtual machine uses a portion of the physical machine's processing, memory and I/O resources. Ideally, server virtualisation provides a means of increasing hardware utilisation.

But as more "logical" servers are consolidated into fewer "physical" computer systems, it's important to protect each virtual machine's data against failure or loss. Virtual servers are the key to providing this protection. This article examines how virtual server backup can be achieved using a mix of traditional backup techniques and specialised virtualisation tools. It also highlights important deployment issues.

What is virtual server backup?

A virtual machine is a complete logical environment existing as a separate entity on a physical server. Each virtual machine is treated and perceived as if it is physical. In fact, a user cannot tell the difference between a real and virtual machine. A data centre may host thousands of virtual machines running on only a fraction of that much hardware, and this presents a serious problem for storage or backup administrators. Data loss on a virtual server can be just as catastrophic as data loss on a physical server, so every virtual server must be backed up as part of a company's backup regimen.

Virtual server backups can be accomplished using a traditional approach with conventional backup software. The backup software is simply installed and configured on each virtual machine, and backups will run normally to any conventional backup target, including tape drives, virtual tape libraries (VTL) or disk storage. "That's probably the most popular way that people do it today because it's familiar," says Lauren Whitehouse, analyst with the Enterprise Strategy Group (ESG). "It ensures a consistent backup; it will give you the granular recovery that you're looking for, and it's application-specific."

However, applying traditional backup tactics to virtual server backups does have drawbacks. The most significant problem is resource contention. Backups demand significant processing power, and the added resources needed to execute a backup may compromise the performance of that virtual machine and all virtual machines running on the system. "Don't go for 100% utilisation," says Greg Schulz, founder and senior analyst at the Storage IO Group. Leave some server resources unused to accommodate backup tasks and stagger backup processes so that only one virtual machine is being backed up on any physical system at one time.

Backup process more costly in virtualised environments