The three main topics of LinuxWorld this past week, it seemed to me, were virtualisation, virtualisation and virtualisation.
For those who haven’t come across this before, it’s a technique for splitting up the power of a single machine so that it appears to be several machines - ‘virtual’ machines - each of which can be running a different operating system, have a different network address, and so forth. It goes one stage further than a multi-user system, where several users may each have their own login sessions, but they’re all sharing the same operating system, peripherals, and memory. With virtual machines, in contrast, each logged-in user can believe they have a full machine to themselves.
It’s a model that was popular in the days of mainframes and minicomputers, and has started to come back into fashion in modern datacentres. Operators have been struggling with how best to manage huge numbers of machines, many of which are web or mail servers running at <10% load but still taking floor space, power, air-conditioning. If you allocate virtual machines, instead of real ones, to these things, then you have much more efficient use of your hardware and more flexibility in its allocation. Adding extra memory to a virtual machine, for example, is usually a matter of changing a software setting, rather than opening up cases and plugging in more chips. Creating a new machine for a new customer’s web server involves simply running some scripts or clicking some buttons.
So what’s the downside? Well, in the past, virtualisation software has been proprietary, expensive, and often not very efficient. There was a substantial performance overhead in persuading one machine to look like several, especially with standard PC-type hardware and software.
One of the reasons it’s such a hot topic this year has been that PC hardware and software has started to understand that it might be virtualised, and to provide the facilities to do so more efficiently. But more importantly, the Open Source system Xen has really started to take off. This was created by a research group at the University of Cambridge where I used to work - the same group responsible for the Trojan Room Coffee Pot about 15 years before. The project spawned a startup called XenSource, VC funding followed, a deal with Microsoft, and so on…
Regular readers will know that we’ve been experimenting with VMs for a while because combining them with thin-client terminals like the Nivo can be quite an interesting way to share a PC between several users.
We’ll talk more about this in later posts, but I wanted to let you know that this post is being typed on a Xen virtual machine which is using a Nivo as its terminal, instead of a graphics card…
