Do I really need it?
Often enough, having a single-system image does not make sense. You may want pockets of discrete resources, each serving its own master. This scenario often happens as a result of these three things:
- Monetary – people like the idea that what they paid for is not being used for someone else
- Political – sometimes folks just don’t want to be part of a larger and organized infrastructure that will force them to share the success and failures of others
- Technology – proper technology is not in place to allow such infrastructure to be built
These three and possibly others could be the culprit of why an enterprise-wide infrastructure is not deployed at times.
Segmenting a single-system seems like an oxymoronic way of approaching the problem, but it will make the users happy. The idea is that a single infrastructure is built-out, but access to the infrastructure is controlled by many entry points as shown in figure 3.
Figure 3: Segmenting a Single-System
From the users’ perspective, each has a dedicated environment. From the infrastructure management point of view, there is a single infrastructure. AS one might expect, this is not ideal as the resource manager makes the best decision from what it knows and not a global view – commonly known as the local maxima problem.
SSI makes perfect sense for Grid, but this greatness comes at a great cost: years of work. This is a repetitive process, where at times, one needs to take a step back in order to take two steps forward. Keep in mind that a single-system-image can only be achieved if the idea is sold to the users and all participants see the benefit that it brings.