Blade servers are being used to provide mission-critical services where server outages can be costly, as much as millions of dollars per hour. A basic blade server with minimal fault tolerance, but implemented with a high level of design quality, is only capable of an average unplanned system downtime of 20 to 25 minutes per year. However, this estimate excludes denial of service attacks. When this cause is included, the unplanned system downtime can increase to 30 to 300 minutes per year depending on target desirability and the effectiveness of the security protection features.