All the posters are stuck on the fact that 100% availability is impossible. But why not instead try to learn from others who offer 100% availability, like Racks

All the posters are stuck on the fact that 100% availability is impossible. But why not instead try to learn from others who offer 100% availability, like Rackspace and SoftLayer? These (legitimate) providers know 100% availability is not possible, but they guarantee it anyway. How can they get away with this? Easy, they have a contractual SLA that indicates what their clients are entitled to when their network fails for any period of time. Further, neither is a low-cost provider, which allows them to engineer their systems to reduce incidences when clients will invoke the SLA. Note that this doesn't mean that Rackspace is shady because they promise 100% knowing they can't deliver it. After all, they put their money where their mouth is! They have an incentive to actually achieve 100% uptime. I'm sure there are other applications where the target is 100% (not 5 nines) availability, especially in finance, medicine, and militaries. My recommendation would be to take your engineering hat off, replace it with a business hat, and provide them with a series of price quotes for various uptime SLAs. And then make sure you're pricing high enough that when something goes down for any period of time that you can make good on your obligations under the SLA without losing too much sleep. Then let the client choose the SLA that matches their business needs and budget.