Last week, I looked at the various types of virtualisation:

Hardware Virtualisation VMware), Para-Virtualisation (Xen) and

OS-Virtualisation (Linux Vserver) with the various merits and vices of each. After

looking at what virtualisation actually is, I think it’s important to look at

why one would want to virtualise and consolidate multiple hardware platforms

into one.

So why virtualise? Because everyone else seems to be doing

it? I hope not! Most server systems are under-utilised; general estimates

say that an average Windows server is running at around 15% utilisation and

UNIX environments at about 20-30%. That’s pretty low. In order to gain a more

personal analysis, I ran a small audit of six servers. All run Linux and host

various high-demand services such as mail serving, mail routing/scanning, file

serving, web services, and database hosting. The results were interesting. Two

servers showed intense usage–one server had constant usage of 90-98% (may be

time to upgrade this one) and the other fluctuated with the norm being 10% but

regular peaks of 65% were observed. A third server showed an average usage of

10% with irregular peaks to 20% utilisation; the remaining three systems were

showing very low utilisation of 0-5%. These last four servers could be good candidates

for virtualisation. Why? Well, with combined peak utilisation of 35% and an

average figure of just 20% they can happily run on one physical platform

without encountering performance problems.

Other than increased

utilisation of resources, what benefits would be gained migrating from these

four systems on to one physical server?

Saving physical space

is the most obvious answer—as a rule, our server rooms don’t grow along in sync

with demands from the business. Unless the entire company is considering an

office move, IT departments will have to work within their given space despite

increases in demand. It’s obvious that replacing four 2U servers with one more

powerful 2U server is going to free up 6Us of space, although this is

optimistic, and realistically 4Us would be freed (I’ll explain the grounds for

this later). This is still a huge saving in real estate and will enable twice

the number of services to be hosted in the same physical space. Many firms

turning to virtualisation will look at moving to blade servers at the same time

to maximise space savings.

Reduced hardware costs are another advantage of virtualisation. In the

example of my four under-utilised systems, all could be migrated to one server

of the same specifications and still have adequate resources—that’s at 25% of

the current hardware cost. Even if I were to over-spec the new system to allow

for future increases in usage, the savings are not to be ignored.

Reduced power consumption and need for cooling are benefits which come hand in hand. While the power

consumption and heat output of a system with high levels of utilisation will be

greater than that of a system under a lesser load, the consolidation of

multiple low-load systems should still produce less heat and demand less power

over all. Data centres are finding it increasingly more difficult to keep up

with demand for power at the rack and the cooling demand which comes with

increased power consumption (and that additional cooling also requires power,

increasing overall running costs).

The ability to rapidly deploy a new system without
ordering new hardware
, building/installing the server, and updating

firmware can be a big time saver for sys admins (whose time is usually at a


Although the above does not give an in-depth explanation of

the many advantages afforded by virtualisation, I hope it gives an informative

overview of benefits when compared to the more traditional server farm model. There

is an abundance of information to be found on both TechRepublic and Google,

this briefing should give those interested in the topic a starting point for

further research. I was hoping to also discuss the potential weaknesses of

virtualised services and the conceivable actions which can help to neutralise

these risks (and in some cases make virtualisation a more solid and lower-cost

approach)—however, I seem to have run short of time so will look at this next

week rather than hastily fumbling over the subject now.

If you have recent experience of consolidating

services with virtualisation, please share your experiences with us all. Were

problems encountered during planning/migration? Has the new virtualised model

realised the benefits expected beforehand?