Fault-tolerant server means less downtime

In July 2001, San Diego Fire & Life Safety Services (SDFLSS) upgraded its computer-aided dispatch (CAD) system for 911 emergency calls. By performing the upgrade, the department has decreased computer downtime.

SDFLSS schedules regular hardware upgrades every three years to ensure the 911 system is dependable and able to accommodate growing call volumes. “Since we [respond to] approximately 95,000 [fire, medical and lifeguard emergency calls] a year, there is never a good time for a system to be out of service,” says Tracy Jarman, deputy chief for SDFLSS.

SDFLSS previously used two servers that were paired in a cluster; if one server failed, the other would take over the workload. While the clustered servers provided 99.5 percent uptime for CAD, the department’s staff was not satisfied with the complexity of installing, testing and administering two servers instead of one.

The clustered servers also required recovery time whenever the hardware “failed over” to another computer processing unit (CPU). (Fail over refers to the time that elapses while a cluster transfers processing from a faulty server to a backup server that is functioning normally.)

SDFLSS staff decided to purchase a fault-tolerant server (ftServer), which provides 99.99 percent CAD availability, from Maynard, Mass.-based Stratus Technologies. The ftServer replicates each of its major components at least once. If its self-diagnostics indicate a problem with any part of the system, a duplicate element continues processing without interruption.

The system powers a dispatch database that supports applications on which the city’s fire and medical personnel depend. For example, the system allows firefighters and paramedics to receive calls on mobile data terminals mounted inside their vehicles. It also drives an automated vehicle locator tied into a global positioning system for dispatch of the closest response unit.

The fault-tolerant CAD system also relays incident details to pagers carried by emergency response personnel and responds to queries from wireless personal digital assistants carried by the department’s administrative staff. In addition, fire department battalion chiefs can view real time and historical event information directly from Web browser screens.