All the dire predictions for the demise of cloud computing that came with yesterday’s GMail downtime were, to be honest, kinda comical. I mean, after all, its not like my Windows laptop ever needs rebooting or the Exchange server ever goes off-line.However, for cooler heads, it does bring up a good question: what are reasonable availability requirements for a cloud based app? Should they be any different (higher or lower) than for an app sitting on a server in your data center.Last week, I talked about the need for cloud service providers to cultivate trust as part of a successful business model, and setting and meeting expectations around availability is certainly part of that.So, what would you want to hear from a cloud service provider that would make you feel comfortable handing over some application workload?I think the simplistic answer is 100% uptime or”5 9s”. I think cell phones long ago showed that the decision making process is a bit more complicated than that: cell phones regularly drop calls and have mediocre voice quality compared to landlines, but they give us convenience, so for most consumers, the trade-off is worth it.Sure you might have apps that need near 100% uptime, but if you need that level or control, and you have that level of utilization, as I mentioned last week, those apps are probably not good candidates for the cloud anyway. So, what kind of trade-off (lower cost, increased functionality) are you willing to accept in return for lowered application availability?