??? High.availability.(system.orientation):.Internet-based services and businesses need
always-on availability. In availability management, hardware or software faults are
unavoidable, and the system is designed to anticipate and work around faults before
they become system failures. Thus, instead of counting on the hardware to avoid faults,
availability and especially the high availability design relies heavily on management
software to mask and manage faults that are expected to occur (Service Availability,
2000). Fault management takes practical precedence over designing for fault avoidance;
the goal is to anticipate faults and execute fault recovery as quickly as possible. In the
race towards ever greater levels of system availability, providing the quickest possible
recovery times becomes the key. Availability management software must execute the
fastest possible switchover to redundant resources and immediate reconfiguration of
the system. In addition, 5-Nines levels of system availability cannot tolerate downtime
for upgrading or maintenance. High availability management must be able to handle
hardware and software upgrades without taking the system out of service. These
requirements all are necessary to providing system availability, but they do not fully
account for the needs of customers using the systems.
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