99.5%? Thats nearly 2 days of downtime a year. I think that most business critical systems would normally be defined as 5 9's (99.999%) which is just over 5 minutes of downtime per year. I have run 'not really critical systems' in the past where the expectation is 4 9's (99.99) which is less (<1 hour/year) (~3157 seconds) and at 3 9's (99.9%) (<9 hours/year), I would have been asked to 'seek opportunities elsewhere'.
My current server system isn't so critical but it has well past 4 9's and I only admin it very part time. Needless to say it doesn't run a Microsoft OS.
In fact it has had less than 2 hours of unplanned downtime in 5 years and thus I would consider it 4 9's.
