No, I think you have it exactly backwards, or at least you're missing an important nuance. It's really, really expensive to duplicate everything across two (or more) data centers. And it's full scope increase in IT costs: most or all cost categories increase. We're talking more than double the costs, in round numbers. Beyond the cost, it's very hard technically to recover hundreds or thousands of servers simultaneously or even near-simultaneously, because you are typically trying to recover not hundreds or thousands of atomistic, independent servers but all the moment-in-time state and functional dependencies among servers. Very, very difficult, which also means hugely expensive and prone to error. Unfortunately, service interruptions are also extremely expensive. What to do?
You could just buy a pair of mainframes, one at site one and the other (configured with reserve capacity, which is lower cost) at site two. (More only if you need the capacity. Then they just operate like a single machine.) That all works really, really well. As in, credit card holders would have no clue that site #1 just burned to the ground -- the credit cards still keep working. That particular form of consolidation makes disaster recovery a relative breeze. DR is just thoroughly baked into the DNA of such equipment, and the very computing model itself supports rapid recovery. (Down to zero interruption effectively and zero data loss, if that's what you need. Or, in DR lingo, RPO and RTO of zero.)
The critical nuance here is if you only consolidate sites, which a lot of businesses have done, you're reducing business resiliency, ceteris paribus. Yes indeed, if you merely forklift your hundreds or thousands of servers into a smaller number of data centers and do basically nothing to consolidate applications, databases, operating system images, etc., onto better DR-protected assets, then disaster recovery will be much tougher and much more expensive. Site-wide disasters will be more disastrous. The game-changer (otherwise known as re-learning time-tested lessons
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