One of the biggest misconceptions regarding failover software, also sometimes referred to as clustering or high availability, is that it guarantees availability. Failover software cannot eliminate all outages or problems, but it can provide additional availability when it comes to hardware failures.
There are two main aspects to architecting a high availability solution:
MTBF—Mean Time Between Failures— How much time elapses on average between each failure.
MTTR—Mean Time To Repair (or Recover)— How quickly the system comes back up and is available for users after a failure occurs.
Unfortunately, many people put too much emphasis on the MTBF figure at the expense of the MTTR figure. Take for example ...