It’s been five years(!) since the last time I asked about your target uptimes for your critical SQL Server instances and I think we’d all be interested to see how things have changed.

Edit 6/2/14: The survey is closed now – see here for the results.

So I present four surveys to you. For your most critical SQL Server instance:

• If it’s a 24×7 system, what’s the target uptime?
• If it’s a 24×7 system, what’s your measured uptime over the last year?
• If it’s not a 24×7 system, what’s the target uptime?
• If it’s a 24×7 system, what’s your measured uptime over the last year?

You’ll notice that the surveys are termed in percentages. Here’s what the percentages mean for a 24×7 system:

• 99.999% = 5.26 minutes of downtime per year
• 99.99% = 52.56 minutes of downtime per year
• 99.9% = 8.76 hours of downtime per year
• 99.5% = 1.825 days of downtime per year
• 99% = 3.65 days of downtime per year
• 98.5% = 5.475 days of downtime per year
• 98% = 7.3 days of downtime per year
• 95% = 18.25 days of downtime per year

If your target uptime allows for planned maintenance downtime, then that doesn’t count as unplanned downtime, as long as your system was only down for the length of time allowed. But don’t cheat yourself and retroactively classify unplanned downtime as planned, so it doesn’t affect your actual, measured uptime.

For instance, if you have a 99.9% uptime goal for a 24×7 system, with a quarterly 4-hour maintenance window, then I would select 99.9% in the 24×7 target survey. For that same system, if the downtime was limited to the proscribed 4-hour window each quarter, and there was no other downtime *at all*, I would select 99.999% on the 24×7 measured uptime survey.

Basic advice is to use common sense in how you answer. If you say you have a 24×7 system but you have a 12-hour maintenance window each week, I wouldn’t classify that as a 24×7 system.

# 24×7 Systems

Survey 1: 24×7 system target uptime

Survey 2: 24×7 system measured uptime
Please be honest. Remember if you choose 99.999% that means you’re saying your system was up for all but 5 minutes in the last year.

# Non-24×7 Systems

Survey 3: Non-24×7 system target uptime