Weighing The Scale

Much of the time in class today was spent talking about scalability.  Scalability is an interesting game because there are many ways to build scale into an infrastructure.

One approach is to build fewer, higher powered hosts. This is known as “scale up” architecture.  With this architecture there are fewer hosts to manage and a higher virtual machine density.  One obvious disadvantage to this is that any single host failure will have a greater impact on the overall infrastructure.  Another approach is to build many lower powered hosts. This is known as “scale out” architecture.  With this architecture there are more hosts to manage. However, virtual machine density will be small, so a host failure will have less of an impact on the overall infrastructure.

In my opinion, there needs to be a combination of both. There is a delicate balance between scale up and scale out. Too much scale up and there is a greater chance of a failure taking down a critical service. Too much scale out and the density of virtual machines becomes so low that virtualization almost becomes meaningless (aside from the benifits of high availability).  I believe this balance will be different in every environment. It is the most important piece of information to determine in any project, yet it is often very difficult and can have long standing effects.

So the question becomes: scale up or scale out, or a combination of both?