Chapter 2. Overview of high availability concepts 15
availability on the order of, for example, 24x7x365 availability, the duration of a
planned outage can be minimized by applying techniques such as rolling
upgrades for software and hot replacement of hardware. Additionally, these
events can be scheduled during periods of lighter system load.
Reasons for planned outages include:
The installation of software upgrades or patches
Periodically scheduled backups
Hardware repairs or expansions
The physical movement of applications of hardware
Unplanned outages are the more urgent concern as they may occur at a time
when the system is required to be operational. The major contributors to
unplanned downtime are:
Hardware failure
Software ...