Monday, June 20, 2011
Difference Between Dataguard and Standby
There is common confusion about oracle standby database and dataguard. I found many people who consider dataguard and standby are same . Here are the difference between Dataguard and standby :
Dataguard : Dataguard is mechanism/tool to maintain standby database. Data Guard provides a comprehensive set of services that create, maintain, manage, and monitor one or more standby databases to enable production Oracle databases to survive disasters and data corruptions. Data Guard maintains these standby databases as copies of the production database. Then, if the production database becomes unavailable because of a planned or an unplanned outage, Data Guard can switch any standby database to the production role, minimizing the downtime associated with the outage.
The dataguard is set up between primary and standby instance .DataGuard can manage both physical and logical standby. DataGuard requires the enterprise edition, while we could write our own standby scripts using the standard edition. we have got support and testing issues-- if something goes wrong, we are on our own to debug our scripts. If we are using DataGuard, there is a variety of documentation available and a variety of options for support. Oracle has also invested quite a bit of time testing DataGuard with various failure scenarios-- it's likely that we wouldn't have that much time to test our own scripts. On a day-to-day basis, DataGuard provides integration with various monitoring utilities (i.e. Enterprise Manager) and provides a rather nice set of tables to view information about what's going on. DataGuard also provides functionality like the ability to automatically detect and resolve gaps in the archived log files that your scripts would not likely be written to handle. And, of course, our scripts could only manage a physical standby database.
Data Guard was originally a set of scripts, but now is the entire environment including a set of processes that control the extraction of redo (directly from log bugger, from redo logs or archive redo logs) from the primary, shipping to the standby, ensuring that the logs are applied. Data Guard processes also include the mechanics needed to make the standby database active automatically (failover) or manually (switchover) and also to re-sync and make the original database active again (switchback).
All that said, Data Guard is only available on Enterprise Edition. Standby capability is available on Standard Edition. And there are commercial products around that provide capability similar to Data Guard for Standard Edition. For more detail click here
Standby Database : Physical standby database provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis. The database schema, including indexes, are the same. A physical standby database is kept synchronized with the primary database, though Redo Apply, which recovers the redo data received from the primary database and applies the redo to the physical standby database. A physical standby database can be used for business purposes other than disaster recovery on a limited basis.