Comment Articles

Virtual computing offers real benefits, real challenges

Rupert Goodwins ZDNet.co.uk

Published: 29 Apr 2004 12:55 BST

The magic word for today is virtualisation. IBM has launched its Virtualization Engine, and you can't find a tech company on the planet that doesn't pay at least lip service to the idea. Briefly put, with virtualisation you can make one chunk of hardware look like multiple independent machines and thus run two copies of Windows, three of MacOS and a brace of Linuxes all at the same time. That's not what gets IBM excited about it, though: it's keen because you can run lots of servers on one box where previously you were limited to one processor and one lot of software.

At first, this seems too good to be true: if you can run ten servers on the same chunk of hardware that previously managed just the one, will you end up buying 90 percent fewer boxes? Quite the opposite, of course: you never get something for nothing, especially not from a company whose sole purpose is to sell you stuff. If you've got one server running on a computer where every resource is maxed out -- processor gasping for breath, disk heads twitching like a Los Angeles seismograph, memory chocka and networks screaming -- then virtualisation will only make things worse.

However, this is rarely the case. Long before all your resources are full, some component will start to limit throughput and start the law of diminishing returns. A common rule of thumb is that a PC-based server starts to run out of steam after about 30 percent of its resources are engaged: virtualisation can help here by allowing different tasks to use the underutilised resources that would otherwise be hanging around waiting for the overstressed stuff to finish.

Eventually there'll be nothing left to maximise, and here's where the benefits of virtualisation kick in. Say you're running four virtual machines on a single piece of silicon -- four web servers, for the sake of argument -- and demand is such that performance is unacceptable. By moving just one of those servers off to fresh hardware, performance for all will be hugely improved -- without having to touch three of them. By increasing the degree of control that managers have over where and how servers run, virtualisation should mean that you end up just buying the kit you actually need, not the amount you need to compensate for the basic inefficiencies of the PC architecture.

There are plenty of other advantages. A virtual environment is just a mix of software and data, so not only can it be moved from machine to machine, it can be backed up on disk, duplicated, transmitted across the Net and so on -- making it much easier to handle in general. Even for individual users, the ability to run multiple operating systems or move complete set-ups from one computer to another will solve a lot of the headaches we have in our daily digital lives.