Virtualisation is a word bandied around by managers as some kind of Holy Grail, able to improve the design of any system, save you money, save the cheerleader and save the world. As you may already have guessed, this is not the case. It is true, however, that virtualisation can bring a host of benefits to a datacentre environment. The problem is that virtualisation is often 'chosen' as the cure-all solution because it is popular, rather than because the advantages it brings have been considered and weighed against the disadvantages.
For the project I have been working on for the last couple of months, consolidating all of the various backup systems around the business and bringing them together into a centralised system, I had the chance to get involved with some fairly new virtualisation software and in the process, understand a lot more about what virtualisation can and can't do for a business.
I'll apologise straight off the bat, I tried to make this blog a bit less technical and failed, sorry 
Before we get onto the advantages and disadvantages of virtualisation, an introduction to the technology we are using that inspired this blog.
The technology chosen for the project was Solaris Logical Domain Technology (shorted to LDOM). This is not the only solution available by any means (Xen and VMWare are two popular alternatives), but it has a few advantages that swung it for us after considering the available options:
The Hardware
The current generation of Niagara processors allow for silly levels of virtualisation if necessary, and a lot of bang for your buck to boot. As an example, take a Sun 5120.
Let’s populate it with a single 1.2GHz T2 processor (64 1.2GHz processing threads, treated as individual CPU's in the virtualised environment) and 64GB of RAM. You could partition this down to as many as 64 separate virtual machines, although more likely you choose, for example, to go for 10 very high performance virtual servers (10 CPUs and 10GB RAM with some resource left over for the underlying system).
Compare this with a Dell 1950, with a pair of 2.5GHz Inter QuadCore processors (8 2.5GHz processing threads) and you would find that it is less powerful 'per server', ends up using more power and costs more to buy if you want to achieve the same level of performance (note that the 1950 does have more single thread oomph).
There are more powerful alternatives available if necessary, such as the 5240, and when the much touted 'Rock' processor family eventually sees the light of day the available processing will only improve and the single thread processing power that the Sun kit lacks should be greatly improved.
Operating System Support
As much as Solaris as an operating system has its advantages in a number of applications, sometimes it really isn't the right choice. Lack of a decent package management and a host of idiosyncrasies mean that a lot of the time you want to use another operating system.
Thankfully for us, then, the LDOM technology supports either Solaris or Ubuntu inside the virtual servers. This sits perfectly with the majority of systems used at PlusNet (using either Solaris 10 or Debian, which is the foundation of Ubuntu and can effectively be interchanged with only minor tweaking).
Here we see one drawback of the LDOM technology. If you were running in a Windows-centric environment its the wrong choice, same if you are tied to something like RedHat Enterprise by the software you use.
Licensing Costs
Yes, the cheapest options is not always the best ... but isn't it nice when its free! All the Logical Domain software is free and will eventually be fully Open Source (the source code for the management software, ldm, is still closed, but they are working to get this open to the community in the near future).
Data Separation
An obscure, but key, advantage of the Logical Domain technology (over, for example, Solaris Zones) is the complete separation of the virtual machines. This means that you can't see the traffic and data in one virtual server if you manage to get access to another virtual server on the machine.
For this project we are backing up from every corner of the network, so the need to separate the backups from the servers that touch customer data (that are locked away behind extra firewalls) from backups that do not is paramount - hence the need for separation (this is a requirement of the PCI standards).
That’s about it as far as an introduction to the technology goes. If you are interested then the there is a lot more on the Sun website (although you do need a server that supports it if you want to try it!). Now we are using the platform in anger I have got to say I am impressed, with the software living up to expectations admirably.
Next week, I’ll be back to start discussing the advantages and disadvantages of virtualisation, starting with how you might be able to save your wallet.
Virtualising the Datacentre #2 - Saving with Virtualisation?