Oracle Database 10 g : Data Guard Administration 1 -
Oracle Database 10 g : Data Guard Administration 1 - Causes of Data Loss According to a survey published in the Disaster Recovery Journal (DRJ), the leading causes of data loss were not natural disasters but hardware failures and human errors. The goal of Oracle Data Guard is to provide an effective safeguard against data loss. Data Guard provides enterprises with complete data protection, data recovery, and data availability, ensuring round-the-clock business continuity.
Oracle Database 10 g : Data Guard Administration 1 - Understanding the Causes of Downtime Every system faces both unplanned and planned downtime. It is important to consider causes of both unplanned and planned downtime when designing a fault-tolerant, resilient infrastructure. Unplanned downtime consists of the following: Computer failures: Downtime occurs when there is a power outage or a system crash. Data failures: Data failure is the loss, damage, or corruption of critical enterprise data. Causes of data failure include: Storage failure: Disk crash or space limitations Human error: Downtime occurs when someone inadvertently drops a table or the system administrator makes an error. Corruption: Caused by a faulty component in the I/O stack Site failure: Downtime occurs when there is some sort of data corruption or natural disaster such as a flood, fire, or earthquake. Planned downtime includes routine operations, periodic maintenance, and new deployments. Planned downtime includes the following: Data changes: Table redefinition and index rebuild System changes: Downtime occurs during hardware and operating-system upgrades.
Oracle Database 10 g : Data Guard Administration 1 - What Is Oracle Data Guard? Oracle Data Guard is a management, monitoring, and automation software infrastructure that works with a production database and one or more standby databases to protect your data against failures, errors, and corruptions that might otherwise destroy your database. It protects critical data by providing facilities to automate the creation, management, and monitoring of the databases and other components in a Data Guard configuration. It automates the process of maintaining a copy of an Oracle production database (called a standby database ) that can be used if the production database is taken offline for routine maintenance or becomes damaged. In a Data Guard configuration, a production database is referred to as a primary database . A standby database is a synchronized copy of the primary database. Using a backup copy of the primary database, you can create from one to nine standby databases. The standby databases, together with the primary database, make up a Data Guard configuration. Each standby database is associated with only one primary database. Note: You can use the Cascaded Redo Log Destinations feature to incorporate more than nine standby databases in your configuration. Refer to the “Other Considerations for Oracle Data Guard” lesson for additional information about this feature.
Oracle Database 10 g : Data Guard Administration 1 - Types of Standby Databases Physical Standby Database A physical standby database is physically identical to the primary database, with on-disk database structures that are identical to the primary database on a block-for-block basis. The physical standby database is updated by performing recovery using redo data that is received from the primary database. The physical standby database can be either recovering data or open for read-only reporting. Logical Standby Database A logical standby database contains the same logical information (unless configured to skip certain objects) as the production database, although the physical organization and structure of the data can be different. The logical standby database is kept synchronized with the primary database by transforming the data in the redo received from the primary database into SQL statements and then executing the SQL statements on the standby database. This is done with the use of LogMiner technology on the redo log information received from the primary database. The tables in a logical standby database can be used simultaneously for recovery and for other tasks such as reporting, summations, and queries. For more information about LogMiner, refer to Oracle Database Utilities .
Oracle Database 10 g : Data Guard Administration 1 - Oracle Data Guard Broker The Oracle Data Guard broker is a distributed management framework that automates and centralizes the creation, maintenance, and monitoring of Data Guard configurations. After the broker creates the Data Guard configuration, the broker monitors the activity, health, and availability of all systems in the Data Guard configuration. You can use Oracle Enterprise Manager Grid Control or the Data Guard broker’s own specialized command-line interface (DGMGRL) to take advantage of the broker’s management capabilities. Enterprise Manager provides a Web-based interface that combines with the broker’s centralized management and monitoring capabilities so that you can easily view, monitor, and administer primary and standby databases in a Data Guard configuration. You can also use the Data Guard command-line interface (CLI) to control and monitor a Data Guard configuration. You can perform most of the activities that are required to manage and monitor the databases in the configuration from the CLI prompt (DGMGRL) or in scripts.
Oracle Database 10 g : Data Guard Administration 1 - Types of Services The following types of services are available with Data Guard: Redo transport services: Control the automated transmittal of redo information from the primary database to one or more standby databases or destinations Log apply services: Control when and how the redo logs are applied to the standby database Redo Apply: Technology used for physical standby databases. Redo data is applied on the standby database by using the standard recovery techniques of an Oracle database. SQL Apply: Technology used for logical standby databases. The received redo data is first transformed into SQL statements, and then the generated SQL statements are executed on the logical standby database. Role-management services: A database operates in one of two mutually exclusive roles: primary or standby. Role-management services operate in conjunction with the redo transport services and log apply services to change these roles dynamically as a planned transition (called a switchover operation ) or as a result of a database failure through a failover operation.
Oracle Database 10 g : Data Guard Administration 1 - Role Transitions: Switchover and Failover Data Guard enables you to change the role of a database dynamically by issuing SQL statements or by using either of the Data Guard broker’s interfaces. Oracle Data Guard supports two role-transition operations: Switchover: The switchover feature provides you with the ability to switch the role of the primary database to one of the available standby databases. The chosen standby database becomes the primary database, and the original primary database then becomes a standby database. Failover: You invoke a failover operation when a catastrophic failure occurs on the primary database and there is no possibility of recovering the primary database in a timely manner. During a failover operation, the failed primary database is removed from the Data Guard environment, and a standby database assumes the primary database role. You invoke the failover operation on the standby database that you want to fail over to the primary role. In Oracle Database 10 g Release 2, you can enable fast-start failover that allows Data Guard to automatically and quickly fail over to a previously chosen, synchronized standby database. Fast-start failover is discussed in detail in the lesson titled “Enabling Fast-Start Failover.”
Oracle Database 10 g : Data Guard Administration 1 - Role Transitions: Switchover and Failover (continued) Databases that have been disabled after a role transition are not removed from the broker configuration, but they are disabled in the sense that the databases are no longer managed by the broker. To reenable broker management of these databases, you must reinstate or re-create the databases. Refer to the lesson titled “Performing Switchover and Failover” for detailed information.
Oracle Database 10 g : Data Guard Administration 1 - Data Protection Modes Data Guard provides three high-level modes of data protection that you can configure to balance cost, availability, performance, and transaction protection. You can configure the Data Guard environment to maximize data protection, availability, or performance. Maximum Protection This protection mode guarantees that no data loss occurs if the primary database fails. To provide this level of protection, the redo data that is needed to recover each transaction must be written to both the local online redo log and the standby redo log (used to store redo data received from another database) on at least one standby database before the transaction commits. To ensure that data loss does not occur, the primary database shuts down if a fault prevents it from writing its redo stream to at least one remote standby redo log. For multiple-instance Real Application Clusters (RAC) databases, Data Guard shuts down the primary database if it is unable to write the redo records to at least one properly configured database instance.
Oracle Database 10 g : Data Guard Administration 1 - Data-Protection Modes (continued) Maximum Availability This protection mode provides the highest possible level of data protection without compromising the availability of the primary database. As with maximum protection mode, a transaction does not commit until the redo needed to recover that transaction is written to the local online redo log and to at least one remote standby redo log. Unlike maximum protection mode, the primary database does not shut down if a fault prevents it from writing its redo stream to a remote standby redo log. Instead, the primary database operates in maximum performance mode until the fault is corrected and all the gaps in the redo log files are resolved. When all the gaps are resolved, the primary database automatically resumes operating in maximum availability mode. This mode guarantees that no data loss occurs if the primary database fails, but only if a second fault does not prevent a complete set of redo data from being sent from the primary database to at least one standby database. Maximum Performance (Default) This default protection mode provides the highest possible level of data protection without affecting the performance of the primary database. This is accomplished by allowing a transaction to commit as soon as the redo data needed to recover that transaction is written to the local online redo log. The primary database’s redo data stream is also written to at least one standby database, but that redo stream is written asynchronously with respect to the commitment of the transactions that create the redo data. When network links with sufficient bandwidth are used, this mode provides a level of data protection that approaches that of maximum availability mode with minimal impact on primary database performance.
Oracle Database 10 g : Data Guard Administration 1 - Benefits of Implementing Oracle Data Guard Oracle Data Guard provides the following benefits: Continuous service: With the use of switchover and failover between systems, your business need not halt because of a disaster at one location. Complete data protection: Data Guard guarantees no data loss and provides a safeguard against data corruption and user errors. Redo data is validated when applied to the standby database. Efficient use of system resources: Standby databases can be used for reporting in addition to providing a safeguard for disaster recovery. You can use a logical standby for real-time reporting and the physical standby database for point-in-time reporting. You can also use the physical standby database for backups of the primary database. Elimination of idle standby systems: A standby database does not have to be idle when you implement a logical standby database. This database is open and ready for reporting at all times. Flexible configurations: You can use Data Guard to configure the system to your needs. With the use of protection modes and several tunable parameters, you can tailor the configuration to your needs. Centralized management: You can use Enterprise Manager Grid Control to manage all configurations in your enterprise.
Oracle Database 10 g : Data Guard Administration 1 - Role of Data Guard in a High-Availability Architecture Oracle Database offers many features to protect your system from common types of downtime. This course focuses on the use of Data Guard. Data Guard addresses data failure and disaster recovery in high-availability architectures. Real Application Clusters (RAC) enables you to build highly available and scalable database servers across multiple systems. For more information about Real Application Clusters, you can attend the Oracle Database 10g: Real Application Clusters course or review the Oracle Real Application Clusters Administrator’s Guide . Oracle Database 10 g introduces the Automatic Storage Management (ASM) feature, which provides a vertically integrated file system and volume manager in the Oracle kernel. For additional information about ASM, see Oracle Database Concepts and the Oracle Database Administrator’s Guide . Oracle Database 10 g includes flashback technologies to address human errors, including Flashback Query, Flashback Versions Query, Flashback Transaction Query, Flashback Database, Flashback Table, and Flashback Drop. For additional information about these features, see the Oracle Database Administrator’s Guide . Oracle’s Hardware Assisted Resilient Data (HARD) is a comprehensive program designed to prevent data corruptions before they happen. Refer to Oracle High Availability Architecture and Best Practices for additional information about the HARD initiative.
Oracle Database 10 g : Data Guard Administration 1 - Role of Data Guard in a High-Availability Architecture (continued) There are a number of features in Oracle Database to support planned downtime that encompasses data changes. Tables can be redefined without interruption to users who are viewing or updating the data. Indexes can be added, rebuilt, or defragmented while the tables that they index are being queried or updated. See the Oracle Database Administrator’s Guide for additional information about these features. Oracle Database dynamically accommodates a number of hardware configuration changes. Patches can be applied to a RAC system in a rolling fashion. Oracle Database 10 g supports the installation of database software upgrades (and the application of patchsets) in a rolling fashion by using Data Guard SQL Apply.
Oracle Database 10 g : Data Guard Administration 1 - Oracle Data Guard and Real Application Clusters RAC provides the following for high availability: Rapid and automatic recovery from node failures or an instance crash Increased scalability Oracle Data Guard provides disaster protection and prevents data loss by: Maintaining transactionally consistent copies of the primary database Protecting against data corruption Protecting against user errors Not requiring expensive and complex mirroring of hardware or software RAC is covered in greater detail in the lesson titled “Using Data Guard in a Real Application Clusters Configuration.”
Oracle Database 10 g : Data Guard Administration 1 - Maximum Availability Architecture RAC and Data Guard provide the basis for the database maximum availability architecture (MAA) solution. MAA provides a comprehensive architecture for reducing downtime for scheduled outages and preventing, detecting, and recovering from unscheduled outages. The recommended MAA has two identical sites. The primary site contains the RAC database, and the secondary site contains both a physical standby database and a logical standby database on RAC. Identical site configuration is recommended to ensure that performance is not sacrificed after a failover or switchover. Symmetric sites also enable processes and procedures to be kept the same between sites, making operational tasks easier to maintain and execute. For more information about MAA, refer to the Oracle Database High Availability Overview manual. This course focuses on the Data Guard component of MAA.
Oracle Database 10 g : Data Guard Administration 1 -
Oracle Database 10 g : Data Guard Administration 1 -