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Server Virtualisation An It Energy Case Study

Server Virtualisation - An IT Energy Case Study

A sizeable proportion of all electricity used by businesses is devoted to running their IT systems.  While PCs and laptops are the visible part of this spend, the lion's share of it is spent in data centres where the servers run 24x7, whether or not users are using the services.  It isn't practical to stop these servers in most cases as they are interdependent and even when nobody is at work, they are often busy doing over-night processing, backups and so on.


The use of often hundreds of servers not only directly consumes power but the air conditioning required to remove the heat generated by the servers also consumes a great deal of electricity.


The large number of servers also pose more logistical problems of the physical space that they take up in the data centre, the provision of the large power supply, the cost of replacement servers every 4-5 years as they get old and unreliable, costs of providing yet more servers at a different location to run the service in the event of a disaster...  The list goes on.


In the last two years a new technology has become mainstream that allows many of these issues to be addressed.  This technology is server virtualisation.


The idea has been around for quite a long time.  Apple Macs have had Windows emulators, PCs have had Sinclair Spectrum emulators.  These were programs that made your computer emulate the hardware of a whole other computer and so you could run programs for that computer on yours.  This is a kind of virtual server - one with just software pretending to be hardware.  It's slow though.  An emulated computer is always going to be slower than the real thing but in recent years, server hardware has got so fast that there's often little computational power expended in them doing their single task.  Typically, a web server might only be utilised to less than 20% of its processing capacity.  The rest of the time it sits idle, burning up electricity and keeping the data centre warm.


The aim of server virtualisation is to make use of the spare processing power of modern servers by using one physical server to run multiple emulations of smaller, less powerful servers.  If a typical physical server is only utilised to 20% of its capacity as a single web server, it stands to reason that the same physical server could run at least four emulated web servers, leaving the last 20% of processing power to manage the emulators.


VMWare are the current leaders in the market for such a server virtualisation software.


In a recent project for a client, I analysed their estate of 52 servers.  These were all in the same data centre and used for a variety of typical purposes (domain controllers, print servers, application servers, web servers, databases, e-mail servers).  Supporting these were the usual necessary LAN switches, firewalls and storage systems (SAN disk arrays and tape libraries).


From the clients power report, we knew that all the kit consumed about 30kW of electricity and that they were short of rack space and grid power capacity.  If they were going to expand their IT any more they were going to have to build a bigger data centre and install a bigger grid feed, bigger UPS, bigger air conditioning, bigger everything!


So we looked at virtualising lots of their servers to deliver the same services but with less hardware and at a lower cost.


Some servers can't easily be virtualised (either because they actually do have a lot of work to do or because of obstructive software licensing rules that make it too expensive to load the application being used on a virtual server).  This lead me to identify about 38 servers that were good candidates for becoming virtual servers.


Of these servers we estimated from past history (or measured statistics) the workload of each physical server and converted that into a virtual workload.  Once you have that figure, you can choose new high power servers that will be able to do the same total work plus a margin for the virtualisation software.  It turned out that just three new servers (with four quad core CPUs each) could comfortably do the required work with 30% spare capacity.


While the excluded hardware would still remain, we could also save some power in the network because with three servers replacing 38 old ones, we didn't need so many network ports.  So two 16 port LAN switches could also be turned off.


The overall result was that we could:

  • Free up a lot of rack space - no need for a new data centre.
  • Reduce the IT power consumption from 30kW to 16kW (saving 45% of their electricity)
  • Avoid having to upgrade their power grid.
  • Avoid having to upgrade their air conditioning and reducing the power consumed by it.
  • Reduce future spending on server replacement and maintenance contracts.
  • Reduce our server support charges, as virtual servers are easier to support than lots of physical ones.
  • Make it easier for them to add disaster recovery servers in the future at another location (virtual servers can be copied on a DVD and loaded up on any new physical server in minutes).



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