Do you need a zero downtime data center? Can you afford it?
Most experts will tell you that the cost difference between 4 1/2 9's and 5 9's (the difference between 99.995 % uptime and 99.999 % uptime) is often too expensive to consider. It is actually a math problem; is your cost of downtime higher than the incremental costs of higher availability from your data centers and systems?
All high availability data centers are not created equal. A Rated-4 data center as rated by the Uptime Institute can still have downtime. TIA 942 compliant data centers can have downtime. Outsource and enterprise data center design details have enormous impact on your risk of downtime.
So it's about defining your requirements, then managing risks. Leverage the expertise of an affordable colocation facility. Let the outsource data center worry about facilities risks so you can concentrate on your critical computer systems.