In my current role with EMC, I get the opportunity to talk with a lot of customers as they look towards augmenting their current infrastructure for various reasons. What I am continuously amazed with is the number of customers who would rather add additional equipment/drives/software to aging storage than to look at refreshing into newer technologies.
The fact of the matter is technology continues to advance in leaps in bounds while simultaneously becoming cheaper. Meaning, you can normally purchase more performance, capacity and features/functions for at a fraction of what you paid for the generation you are currently utilizing (think laptops). Then hardware, like any other consumable, has a finite lifespan. Eventually, you will get to a point where you are continuously replacing parts which can be frustrating for the business.
So, when is the right time to migrate? I have done a ton of TCO’s and ROI’s and what I have found is that if you are looking to just maintain status-quo, I.E. make ZERO investment into an aged SAN then financially you are better off staying where you are. But, if you have any needs around adding performance or storage you are almost always better off purchasing a new storage (which includes 3 years of support) than to pay for the additions + the three years of support.