For many applications, availability during business hours is required, but
Database H gh Ava lab l ty: An Extended Survey
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of Idea Group Inc. is prohibited.
some downtime during non-business hours is acceptable. System failure outages can be
caused by environmental causes such as loss of electricity, fires, floods, and earthquakes
in addition to platform failures, application failures, or human errors. Although hardware
failures are traditionally the major cause of downtime, software failures and user error are
growing. Generally there are three types of downtime (Barraza, 2002; Kumar, 2005; Saito,
Bershad, & Levy, 1999):
??? Planned. downtime: This is normal downtime that is planned and scheduled in
advance. It is normally scheduled for patches, upgrades, and maintenance activities
such as database reorganization, adding disk storage, performing offline backups, and
installing patches, upgrades, or new application. It usually occurs during off-peak
processing times such as off-hours or holidays.
??? Semi-planned. downtime: This includes software or hardware upgrades that are
scheduled, but not entirely by the service provider.
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