Genuine 100% uptime is not possible, at least not at this point in time. Networks and servers will always experience downtime, whatever the issue may be (ddos, power outage, nature, terrorism, mistakes, etc.).
Maintenance is generally not included while monitoring uptime.
Haha, I do not even think that is possible to the slightest extent. I been with a host that claimed a hundred percent uptime...but i got downtime. The closest site I ever seen to a full hundred percent is Google.
You can create a rather complicated round robin solution that would give you pretty damn close to 100% uptime, but it's impossible to achieve that. No one (not even sites like Amazon.com and eBay) achieve 100% uptime. Also, keep in mind that each '9' you add after 99.x increases costs exponentially. Not trying to depress you, but uptime is expensive.
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100% is pretty near impossible.
Even if you have redundant everything, there is switchover time while devices learn that the other has failed.
99.99% is doable.
By this I mean that a network can be designed for it. 2 of everything and well coordinated maint. windows can carry 99.99% but anything more and you are getting into the LUCK catagory.
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