I’ve recently upgraded several systems to use the latest server virtualisation software from VMware. The business in question needed the new software primarily so that it could assign over 3.6GB of RAM and more than two processors to its accountancy system, which runs in a virtual machine (VM) under VMware Infrastructure 3 (VI3).

But while the upgrade was easy to justify in its own right, some of the biggest benefits of the move were not apparent until we had the new software up and running.

Besides the much-needed performance boost, the biggest benefit was the updated snapshot feature that captures a VM system image while it is running.

VM snapshots capture the entire state of a virtual machine – the contents of the disk, RAM and various processors – in just a few seconds, while people are simultaneously working on the system.

This makes them incredibly useful. The accountancy system is continuously accessed by workers in Europe, South America and the US, for example, so it is constantly busy throughout the week. This makes scheduling weekday downtime to back it up before applying patches difficult to do, and we previously restricted the task to one weekend or so a month.

With VI3 installed, we use snapshots to make an “instant backup” of the server before applying patches. Once we are happy that adding the patches did not cause a problem, we delete the snapshot, all without taking the server offline.

It is true that if we need to restore the snapshot, we would have to manage any updates to the accountancy data that had been made since the backup was done, and that can add some complexity. Consequently, we try to apply patches while the system is quiet and there are fewer changes to accommodate, but we only need it to be quiet for 15 minutes or so to get this kind of maintenance done.

By comparison, making a full backup of a traditional server could take several hours and would probably require the server to be switched off first. In the event that patching our system did cause a problem, the snapshot backup can be restored in a few seconds.

Because the virtualisation hypervisor has full control over the accountancy server’s access to RAM and disk, the snapshot will restore the system to exactly the same state that it was in when the snapshot was taken – even the screen and mouse are exactly as we left them.

Also, it is important to remember that problems caused by patches being applied are actually rare – in the past year we had only one episode where adding a Windows patch caused our Citrix server to stop accepting connections.