Single Instance or Multiple Instances?
For a global company, choosing between a single instance and multiple instances is a strategic decision which can augment the way the company does business.
While it may seem easy to say that single instance is the right decision, there are merits in multiple instances and a company should think through the merits and demerits before arriving at a decision.
Proponents of single instance have argued that having a single instance leads to lesser maintenance and less troublesome upgrades as we can minimize the complexities of the development and test environments. Also, data flow between multiple instances is never a challenge.
The concept of multiple instances came from 80s when due to server load issues, companies had to resort to separate instances. Changing the architecture is always a painful job once you have added complexities to your instances, hence companies continue with the old architecture. But there are companies which actually maintain multiple instances to take advantage of tax benefits in Europe or US of maintaining data of a particular geography in separate servers. And of course there are instances of classic risk mitigation where companies have global processes to be supported in one instance while local processes (localization needs) go into another instance to minimize the risk to the business (owing to localization patches).
Therefore what seems to be an easy decision in favor of a single instance is not that easy!!!
