The next characteristic of high availability is recoverability. This refers to the ability to overcome a momentary failure in such a way that there is no impact on end-user availability. It could be as small as a portion of main memory recovering from a single-bit memory error, and as large as having an entire server system switch over to its standby system with no loss of data or transactions. Recoverability also includes retries of attempted reads and writes out to disk or tape, as well as retrying of transmissions down network lines.
Responsiveness is the sense of urgency that all people involved with high availability need to exhibit. This includes having well-trained suppliers and in-house support personnel who can respond to problems quickly and efficiently. It also pertains to how quickly the automated recovery of resources such as disks or servers can be enacted.
The final characteristic of high availability is robustness, which describes the overall design of the availability process. A robust process is able to withstand a variety of forcesboth internal and externalthat could easily disrupt and undermine availability in a weaker environment. Robustness puts a high premium on documentation and training to withstand technical changes related to platforms, products, services, and customers; personnel changes related to turnover, expansion, and rotation; and business changes related to new direction, acquisitions, and mergers.
Understanding and applying these seven characteristics of high availability can help transform the continuous uptime of your infrastructure into what may be the most significant R of all: reality.