IBM AIX Continuous Availability Features - IBM Redbooks

1.5 Continuous operations
Continuous operations is an attribute of IT environments and systems which allows them to
continuously operate and mask planned outages from end users. Continuous operations
employs non-disruptive hardware, software, configuration and administrative changes.
Unplanned downtime is an unexpected outage and often is the result of administrator error,
application software failure, operating system faults, hardware faults, or environmental
disasters.
Generally, hardware component failure represents an extremely small proportion of overall
system downtime. By far, the largest single contributor to system downtime is planned
downtime. For example, shutting down a computer for the weekend is considered planned
downtime. Stopping an application to take a level 0 (full) system backup is also considered
planned downtime.
1.6 Continuous availability
Continuous availability is an attribute of a system which allows it to deliver non-disruptive
service to end users 7 days a week, 24 hours a day by preventing both planned and
unplanned outages.
Continuous availability (Elimination of downtime) = Continuous operations (Masking or
elimination of planned downtime) + High availability (Masking or elimination of unplanned
downtime)
Most of today’s solutions are based on an integration of the operating system with clustering
software, storage, and networking. When a failure is detected, the integrated solution will
trigger an event that will perform a predefined set of tasks required to reactivate the operating
system, storage, network, and in many cases, the application on another set of servers and
storage. This kind of functionality is defined as IT continuous availability.
The main goal in protecting an IT environment is to achieve continuous availability; that is,
having no end-user observed downtime. Continuous availability is a collective term for those
characteristics of a product which make it:
► Capable of performing its intended functions under stated conditions for a stated period of
time (reliability)
► Ready to perform its function whenever requested (availability)
► Able to quickly determine the cause of an error and to provide a solution to eliminate the
effects of the error (serviceability)
Continuous availability encompasses techniques for reducing the number of faults,
minimizing the effects of faults when they occur, reducing the time for repair, and enabling the
customer to resolve problems as quickly and seamlessly as possible.
AIX continuous availability encompasses all tools and techniques implemented at the
operating system level that contribute to overall system availability. Figure 1-1 on page 5
illustrates AIX continuous availability.
4 IBM AIX Continuous Availability Features