Thorsten: If you don’t deploy across AZs for cost reasons then you have lowered your survival chances long ago before even talking about EBS. With EBS down every 3 months, that won't be the experience of many. You're saying the last EBS outage didn't affect any other zones, but for me it did (could be pure coincidence of course, perhaps, had a slave server that had to be rebooted before it worked again), but there were more complaining about this on the forums. Traditional hardware is pretty reliable, easily lasts 3-5 years without any downtime. Your average data centre also can last 4-5 years before a significant outage (and then it's usually multi-day, see Sandy, but there are numerous other examples). My point is that I suspect that many sites have seen more multi-hour outages with AWS than before, more than they were used too perhaps. We probably should offset that against the ability to auto-scale, so you're usually not going down due to traffic volume. Is AWS worth it? That's the question I'm struggling with. Obviously I never want to be in a single data centre hosting environment ever again (had my multi-day outages, Sandy is another example). PS: my estimate for cross AZ traffic is that it adds 20% to the cost.