* DataGuard is a Oracle software component to create/maintain/monitor one or more (up to nine) standby databases.
* Redo log files are transferred (ind sync or async mode) and applied to standby databases.
* Two operation modes
– Redo apply: physical standby
– SQL apply: logical standby. Can be used concurrently for queries for reporting etc.
* Can be managed by SQL*Plus or DataGuard Broker

* Requires same OS (e.g. Linux on Intel) on both primary and standby systems.
* Same release of Oracle Enterprise Edition on both primary and standby systems.

* Primary db goes out
* One of the standby db is brought in as new primary db
* If Flashback Database feature is installed on original primary db,
– original primary db can be bought back as standby db
* If Flashback Database feature is NOT installed on primary db,
– original primary db can ONLY be created from a backup copy of the new primary db

* Planned reversal of primary and standby db