Your “Five Nines” Means Nothing To Me

SQL Server Best Practices
SQL Server Best Practices
There’s a lot of talk on High Availability. I know I’m a huge fan of it, in particular clustering (but I know it’s not for all situations and the changes that SQL 2012 with AlwaysOn Groups may mean that traditional clustering is used less and less). There are of course other HA solutions out there like Log Shipping, Mirroring and SAN replication technologies (sorry folks, I disagree on transactional replication as an HA concept unless you are talking downstream reporting infrastructure behind load balancers).

People constantly push to achieve the magical five nines availability number. What does that mean?

Five nines means that your SQL Server must be available 99.999% of the time. This means you can have only 5.26 minutes of downtime a year.

So let’s say that you are running clustering and mirroring; that you have load balancing with peer-to-peer replication; that you are running SAN replication between two datacenters and have log shipping setup ready to go live at the flick of a switch. You have all your hardware ducks in a row and are ready for any emergency that may crop up.

I commend you for all of that.

Now let’s say that your manager is going to bonus you on the downtime that you have. You are the DBA, a single link in the chain, and your entire bonus is going to based on the number of nines that you can get over the year.

Time to sit down with your manager and ask some questions:

  • Does this five nines bonus plan include maintenance time?
  • How are you going to measure uptime?
  • What tools are going to be used to measure it?
  • What are the tolerances on those tools?
  • What about upstream items?

 Let’s take a look at these one at a time.

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