1 Introduction to Oracle Data Guard
Oracle Data Guard ensures high availability, data protection, and disaster recovery for enterprise data. 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. Data Guard can be used with traditional backup, restoration, and cluster techniques to provide a high level of data protection and data availability.
（Oracle Data Guard可确保企业数据的高可用性，数据保护和灾难恢复。Data Guard提供了一套全面的服务，可以创建，维护，管理和监视一个或多个备用数据库，从而实现Oracle的生产数据库以应对灾难和数据损坏。Data Guard将这些备用数据库维护为生产数据库的副本。然后，如果生产数据库由于计划中断或意外中断而变得不可用，则Data Guard可以将任何备用数据库切换到生产角色，从而最大限度地减少与停机相关的停机时间。Data Guard可以与传统的备份，恢复和集群技术一起使用，以提供高水平的数据保护和数据可用性。）
With Data Guard, administrators can optionally improve production database performance by offloading resource-intensive backup and reporting operations to standby systems.
（借助Data Guard，管理员可以选择通过将资源密集型备份和报告操作卸载到备用系统来提高生产数据库性能。）
1.1 Data Guard Configurations
A Data Guard configuration consists of one production database and one or more standby databases. The databases in a Data Guard configuration are connected by Oracle Net and may be dispersed geographically. There are no restrictions on where the databases are located, provided they can communicate with each other. For example, you can have a standby database on the same system as the production database, along with two standby databases on other systems at remote locations.
（一data Guard配置由一个生产数据库和一个或多个备用数据库组成。Data Guard配置中的数据库通过Oracle Net可能在地理上分散。只要可以，数据库的位置没有限制相互沟通。例如，您可以在与生产数据库相同的系统上有一个备用数据库，以及在远程位置的其他系统上有两个备用数据库。）
You can manage primary and standby databases using the SQL command-line interfaces or the Data Guard broker interfaces, including a command-line interface (DGMGRL) and a graphical user interface that is integrated in Oracle Enterprise Manager.
（您可以使用SQL命令行界面或Data Guard代理程序接口（包括命令行界面（DGMGRL）和集成在Oracle Enterprise Manager中的图形用户界面来管理主数据库和备用数据库。）
1.1.1 Primary Database
A Data Guard configuration contains one production database, also referred to as the primary database, that functions in the primary role. This is the database that is accessed by most of your applications.The primary database can be either a single-instance Oracle database or an Oracle Real Application Clusters (Oracle RAC) database.
（Data Guard配置包含一个生产数据库（也称为主数据库），该数据库在其中起作用 主要角色。这是大多数应用程序访问的数据库。主数据库可以是单实例Oracle数据库或Oracle Real应用集群（Oracle RAC）数据库。）
1.1.2 Standby Databases
A standby database is a transactionally consistent copy of the primary database. Using a backup copy of the primary database, you can create up to thirty standby databases and incorporate them in a Data Guard configuration. Once created, Data Guard automatically maintains each standby database by transmitting redo data from the primary database and then applying the redo to the standby database.Similar to a primary database, a standby database can be either a single-instance Oracle database or an Oracle RAC database.The types of standby databases are as follows:
（standby数据库是主数据库的事务一致副本。使用ab主数据库的备份副本，可以创建多达30个备用数据库，并将它们合并到Data Guard配置中。一旦创建，Data Guard将通过传输自动维护每个备用数据库从主数据库重做数据，然后应用 重做到备用数据库。与主数据库类似，备用数据库可以是单实例Oracle数据库，也可以是 Oracle RAC数据库。备用数据库的类型如下：
）
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, through Redo Apply, which recovers the redo data received from the primary database and applies the redo to the physical standby database.
As of Oracle Database 11g release 1 (11.1), a physical standby database can receive and apply redo while it is open for read-only access. A physical standby database can therefore be used concurrently for data protection and reporting.
（提供与主数据库完全相同的副本 在磁盘数据库结构上，以块为单位，与主数据库相同。数据库模式（包括索引）是相同的。物理备用数据库通过“重做应用”与主数据库保持同步，“重做应用”恢复从主数据库接收到的重做数据，并将重做应用到物理备用数据库。
从Oracle Database 11g发行版本1（11.1）开始，物理备用数据库可以接收并应用重做，只要其以只读方式打开即可。物理备用数据库因此可以同时用于数据保护和报告。）
Contains the same logical information 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 through SQL Apply, which transforms the data in the redo received from the primary database into SQL statements and then executes the SQL statements on the standby database.
A logical standby database can be used for other business purposes in addition to disaster recovery requirements. This allows users to access a logical standby database for queries and reporting purposes at any time. Also, using a logical standby database, you can upgrade Oracle Database software and patch sets with almost no downtime. Thus, a logical standby database can be used concurrently for data protection, reporting, and database upgrades.
（包含与生产数据库相同的逻辑信息，尽管数据的物理组织和结构可能不同。逻辑备用数据库通过SQL应用程序与主数据库保持同步，SQL应用程序将从主数据库接收到的重做数据转换成SQL语句，然后执行备用数据库上的SQL语句。
除了灾难恢复要求之外，逻辑备用数据库还可用于其他业务目的。这允许用户访问逻辑备用数据库查询和随时报告。此外，使用逻辑备用数据库，您可以几乎不停机地升级Oracle数据库软件和补丁集。因此，逻辑备用数据库可以同时用于数据保护，报告和数据库升级。）
A snapshot standby database is a fully updatable standby database.
Like a physical or logical standby database, a snapshot standby database receives and archives redo data from a primary database. Unlike a physical or logical standby database, a snapshot standby database does not apply the redo data that it receives. The redo data received by a snapshot standby database is not applied until the snapshot standby is converted back into a physical standby database, after first discarding any local updates made to the snapshot standby database.
A snapshot standby database is best used in scenarios that require a temporary, updatable snapshot of a physical standby database. Note that because redo data received by a snapshot standby database is not applied until it is converted back into a physical standby, the time needed to recover from a primary database failure is directly proportional to the amount of redo data that needs to be applied.
1.1.3 Configuration Example
Figure 1-1 shows a typical Data Guard configuration that contains a primary database that transmits redo data to a standby database. The standby database is remotely located from the primary database for disaster recovery and backup operations. You can configure the standby database at the same location as the primary database. However, for disaster recovery purposes, Oracle recommends you configure standby databases at remote locations.
Figure 1-1 Typical Data Guard Configuration
1.2 Data Guard Services
The following sections explain how Data Guard manages the transmission of redo data, the application of redo data, and changes to the database roles:
Control the automated transfer of redo data from the production database to one or more archival destinations.
（控制重做数据从生产数据库到一个或多个归档目的地的自动传输）
Apply redo data on the standby database to maintain transactional synchronization with the primary database. Redo data can be applied either from archived redo log files, or, if real-time apply is enabled, directly from the standby redo log files as they are being filled, without requiring the redo data to be archived first at the standby database.
（应用 在备用数据库上重做数据以维持与主数据库的事务同步。重做数据可以从归档重做日志文件中应用，或者，如果实时应用程序在被填充时直接从备用重做日志文件启用，而不需要在备用数据库首先归档重做数据。）
Change the role of a database from a standby database to a primary database, or from a primary database to a standby database using either a switchover or a failover operation.
（使用切换或故障切换操作将数据库的角色从备用数据库更改为主数据库，或从主数据库更改为备用数据库。）
1.2.1 Redo Transport Services
Redo transport services control the automated transfer of redo data from the production database to one or more archival destinations.
Redo transport services perform the following tasks:
Transmit redo data from the primary system to the standby systems in the configuration
Manage the process of resolving any gaps in the archived redo log files due to a network failure
Automatically detect missing or corrupted archived redo log files on a standby system and automatically retrieve replacement archived redo log files from the primary database or another standby database
（重做传输服务执行以下任务：
将重做数据从主系统传输到配置中的备用系统
管理由于网络故障而解决归档重做日志文件中的任何空白的过程
一个自动检测备用系统上丢失或损坏的归档重做日志文件，并自动从主数据库或其他备用数据库中检索替换的归档重做日志文件）
1.2.2 Apply Services
The redo data transmitted from the primary database is written to the standby redo log on the standby database. Apply services automatically apply the redo data on the standby database to maintain consistency with the primary database. It also allows read-only access to the data.
The main difference between physical and logical standby databases is the manner in which apply services apply the archived redo data:
For physical standby databases, Data Guard uses Redo Apply technology, which applies redo data on the standby database using standard recovery techniques of an Oracle database, as shown in Figure 1-2.
Figure 1-2 Automatic Updating of a Physical Standby Database
（从主数据库传输的重做数据写入备用数据库的备用重做日志。应用服务自动应用重做备用数据库上的数据以保持与主数据库的一致性。它也允许只读访问数据。
主要区别 逻辑备用数据库是应用服务应用归档重做数据的方式：
物理备用数据库，Data Guard使用Redo Apply技术，该技术使用Oracle数据库的标准恢复技术在备用数据库上应用重做数据）
For logical standby databases, Data Guard uses SQL Apply technology, which first transforms the received redo data into SQL statements and then executes the generated SQL statements on the logical standby database, as shown in Figure 1-3.
（逻辑备用数据库，Data Guard使用SQL Apply技术，它首先将接收到的重做数据转换成SQL语句，然后在逻辑备数据库上执行生成的SQL语句）
Figure 1-3 Automatic Updating of a Logical Standby Database
1.2.3 Role Transitions
An Oracle database operates in one of two roles: primary or standby. Using Data Guard, you can change the role of a database using either a switchover or a failover operation.
A switchover is a role reversal between the primary database and one of its standby databases. A switchover ensures no data loss. This is typically done for planned maintenance of the primary system. During a switchover, the primary database transitions to a standby role, and the standby database transitions to the primary role.
A failover is when the primary database is unavailable. Failover is performed only in the event of a failure of the primary database, and the failover results in a transition of a standby database to the primary role. The database administrator can configure Data Guard to ensure no data loss.
The role transitions described in this documentation are invoked manually using SQL statements. You can also use the Oracle Data Guard broker to simplify role transitions and automate failovers using Oracle Enterprise Manager or the DGMGRL command-line interface, as described in Section 1.3.
（Oracle数据库以两种角色之一运行：主数据库或备用数据库。使用Data Guard，可以使用切换操作或故障切换操作来更改数据库的角色。
一个 切换是一个主数据库和其中一个备用数据库之间的角色转换。切换确保没有数据丢失。这通常是为主系统的计划维护而完成的。在切换期间，主数据库转换为备用角色，备用数据库转换为主角色。
一个 主数据库不可用时进行故障转移。仅当主数据库发生故障时才执行故障转移，故障转移将导致备用数据库转移到主角色。数据库管理员可以配置Data Guard确保 没有数据丢失。
在本文档中描述的角色转换被调用每次使用SQL语句。您也可以使用Oracle Data Guard代理来简化角色转换并使用Oracle企业管理器或DGMGRL命令行界面自动化故障转移，如第1.3节所述。）
1.3 Data Guard Broker
The Data Guard broker is a distributed management framework that automates the creation, maintenance, and monitoring of Data Guard configurations. You can use either the Oracle Enterprise Manager graphical user interface (GUI) or the Data Guard command-line interface (DGMGRL) to:
Create and enable Data Guard configurations, including setting up redo transport services and apply services
Manage an entire Data Guard configuration from any system in the configuration
Manage and monitor Data Guard configurations that contain Oracle RAC primary or standby databases
Simplify switchovers and failovers by allowing you to invoke them using either a single key click in Oracle Enterprise Manager or a single command in the DGMGRL command-line interface.
Enable fast-start failover to fail over automatically when the primary database becomes unavailable. When fast-start failover is enabled, the Data Guard broker determines if a failover is necessary and initiates the failover to the specified target standby database automatically, with no need for DBA intervention.
In addition, Oracle Enterprise Manager automates and simplifies:
Creating a physical or logical standby database from a backup copy of the primary database
Adding new or existing standby databases to an existing Data Guard configuration
Monitoring log apply rates, capturing diagnostic information, and detecting problems quickly with centralized monitoring, testing, and performance tools
（该 Data Guard代理是一个分布式管理框架，可以自动创建，维护和监视Data Guard配置。您可以使用Oracle企业管理器图形用户界面（GUI）或Data Guard命令行界面（DGMGRL）执行以下操作：
创建并启用Data Guard配置，包括设置重做传输服务和应用服务
从配置中的任何系统管理整个Data Guard配置
管理和监视包含Oracle RAC主数据库或备用数据库的Data Guard配置
简化 转换和 允许您使用Oracle企业管理器中的单键单击或DGMGRL命令行界面中的单个命令来调用它们。
启用 当主数据库变得不可用时，快速启动故障转移自动进行故障转移。启用快速启动故障转移时，Data Guard代理会确定是否需要故障转移，并自动启动故障转移到指定的目标备用数据库，而不需要DBA干预。
另外，Oracle企业管理器自动化和简化：
创建物理或逻辑备用数据库 主数据库的备份副本
将新的或现有的备用数据库添加到现有的Data Guard配置
通过集中监控，测试和性能工具，监控日志应用率，捕获诊断信息并快速检测问题）
1.3.1 Using Oracle Enterprise Manager Grid Control
Oracle Enterprise Manager Grid Control (also referred to as Enterprise Manager in this book) provides a web-based interface for viewing, monitoring, and administering primary and standby databases in a Data Guard configuration. Enterprise Manager's easy-to-use interfaces, combined with the broker's centralized management and monitoring of the Data Guard configuration, enhance the Data Guard solution for high availability, site protection, and data protection of an enterprise.
From the
Central Console of Enterprise Manager Grid Control, you can perform all management operations either locally or remotely. You can view home pages for Oracle databases, including primary and standby databases and instances, create or add existing standby databases,
start and stop instances, monitor instance performance, view events, schedule jobs, and perform backup and recovery operations.
（Oracle企业管理器网格控制（本书中也称为企业管理器）提供了一个基于Web的界面，用于在Data
Guard配置中查看，监视和管理主数据库和备用数据库。企业管理器的易于使用的界面，结合代理对Data Guard配置的集中管理和监控，增强了Data Guard解决方案的可用性，站点保护和企业数据保护。
从企业管理器网格控制的*控制台，您可以执行本地或远程的所有管理操作。您可以查看Oracle数据库的主页，包括主数据库和备用数据库和实例，创建或添加现有备用数据库，启动和停止实例，监视实例性能，查看事件，计划作业以及执行备份和恢复操作。）
1.3.2 Using the Data Guard Command-Line Interface
The Data Guard command-line interface (DGMGRL) enables you to control and monitor a Data Guard configuration from the DGMGRL prompt or within scripts. You can perform most of the activities required to manage and monitor the databases in the configuration using DGMGRL. See Oracle Data Guard Broker for complete DGMGRL reference information and examples.
（Data Guard命令行界面（DGMGRL）使您可以从DGMGRL提示或脚本中控制和监视Data Guard配置。您可以使用DGMGRL执行大部分管理和监视配置数据库所需的活动。有关完整的DGMGRL参考信息和示例，请参阅Oracle Data Guard Broker。）
1.4 Data Guard Protection Modes
In some situations, a business cannot afford to lose data regardless of the circumstances. In other situations, the availability of the database may be more important than any potential data loss in the unlikely event of a multiple failure. Finally, some applications require maximum database performance at all times, and can therefore tolerate a small amount of data loss if any component should fail. The following descriptions summarize the three distinct modes of data protection.
（在某些情况下，不管情况如何，企业都不能丢失数据。在其他情况下，数据库的可用性可能比任何可能发生的多重故障事件中的潜在数据丢失更为重要。最后，一些应用程序始终需要最大的数据库性能，因此如果任何组件出现故障，可以承受少量的数据丢失。以下描述总结了三种不同的数据保护模式。）
Maximum availability This protection mode provides the highest level of data protection that is possible without compromising the availability of a primary database. Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to the standby redo log on at least one synchronized standby database. If the primary database cannot write its redo stream to at least one synchronized standby database, it operates as if it were in maximum performance mode to preserve primary database availability until it is again able to write its redo stream to a synchronized standby database.
This protection mode ensures zero data loss except in the case of certain double faults, such as failure of a primary database after failure of the standby database.
（最大可用性 此保护模式提供了*别的数据保护，而不会影响主数据库的可用性。事务不会提交，直到恢复这些事务所需的所有重做数据已写入联机重做日志和至少一个同步备用数据库上的备用重做日志。如果主数据库无法将其重做流写入至少一个同步备用数据库，则它将像处于最高性能模式一样运行，以保留主数据库的可用性，直到它再次能够将其重做流写入同步的备用数据库为止。
这种保护模式可以保证零数据丢失，除了在某些双重故障情况下，例如备用数据库故障后主数据库发生故障。）
Maximum performance This is the default protection mode. It provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log. Redo data is also written to one or more standby databases, but this is done asynchronously with respect to transaction commitment, so primary database performance is unaffected by delays in writing redo data to the standby database(s).
This protection mode offers slightly less data protection than maximum availability mode and has minimal impact on primary database performance.
（最高性能 这是默认的保护模式。它提供了可能的*别的数据保护，而不会影响主数据库的性能。这是通过允许事务一旦所有由这些事务生成的重做数据被写入在线日志来提交的。重做数据也被写入到一个或多个备用数据库，但是这是针对事务处理的异步完成的，所以主数据库的性能不会受到向备用数据库写入重做数据的延迟的影响。）
Maximum protection This protection mode ensures that no data loss will occur if the primary database fails. To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to the standby redo log on at least one synchronized standby database before the transaction commits. To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions, if it cannot write its redo stream to at least one synchronized standby database.
（最大保护 此保护模式确保主数据库发生故障时不会发生数据丢失。为了提供此级别的保护，在事务提交之前，恢复事务所需的重做数据必须写入至少一个同步备用数据库的联机重做日志和备用重做日志。为确保不会发生数据丢失，如果主数据库无法将其重做流写入至少一个同步备用数据库，则主数据库将关闭，而不是继续处理事务。）
All three protection modes require that specific redo transport options be used to send redo data to at least one standby database.
（所有这三种保护模式都要求使用特定的重做传输选项将重做数据发送到至少一个备用数据库。）
1.5 Client Failover
A high availability architecture requires a fast failover capability for databases and database clients.
Client failover encompasses failure notification, stale connection cleanup, and transparent reconnection to the new primary database. Oracle Database provides the capability to integrate database failover with failover procedures that automatically redirect clients to a new primary database within seconds of a database failover.
高可用性体系结构要求数据库和数据库客户端具有快速故障转移功能。
（客户端故障转移包括故障通知，陈旧的连接清理和透明的重新连接到新的主数据库。Oracle数据库提供了将数据库故障转移与故障转移过程相集成的功能，可在数据库故障转移的几秒钟内自动将客户端重定向到新的主数据库。）
1.6 Data Guard and Complementary Technologies
Oracle Database provides several unique technologies that complement Data Guard to help keep business critical systems running with greater levels of availability and data protection than when using any one solution by itself. The following list summarizes some Oracle high-availability technologies:
Oracle Real Application Clusters (Oracle RAC)
Oracle RAC enables multiple independent servers that are linked by an interconnect to share access to an Oracle database, providing high availability, scalability, and redundancy during failures. Oracle RAC and Data Guard together provide the benefits of both system-level, site-level, and data-level protection, resulting in high levels of availability and disaster recovery without loss of data:
Oracle RAC addresses system failures by providing rapid and automatic recovery from failures, such as node failures and instance crashes. It also provides increased scalability for applications.
Data Guard addresses site failures and data protection through transactionally consistent primary and standby databases that do not share disks, enabling recovery from site disasters and data corruption.
Many different architectures using Oracle RAC and Data Guard are possible depending on the use of local and remote sites and the use of nodes and a combination of logical and physical standby databases.
（Oracle RAC支持通过互连链接的多个独立服务器共享对Oracle数据库的访问，从而在故障期间提供高可用性，可伸缩性和冗余性。Oracle RAC和Data Guard一起提供系统级，站点级和数据级保护的好处，从而实现高水平的可用性和灾难恢复，而不会丢失数据：
Oracle RAC通过提供从故障（例如节点故障和实例崩溃）的快速和自动恢复来解决系统故障。它还为应用程序提供了更高的可伸缩性。
Data Guard通过不共享磁盘的事务一致主数据库和备用数据库来解决站点故障和数据保护问题，从而实现站点灾难恢复和数据损坏。
使用Oracle RAC和Data Guard的许多不同体系结构是可能的，具体取决于本地和远程站点的使用以及节点的使用和逻辑和物理备用数据库的组合。）
Flashback Database
The Flashback Database feature provides fast recovery from logical data corruption and user errors. By allowing you to flash back in time, previous versions of business information that might have been erroneously changed or deleted can be accessed once again. This feature:
Eliminates the need to restore a backup and roll forward changes up to the time of the error or corruption. Instead, Flashback Database can roll back an Oracle database to a previous point-in-time, without restoring datafiles.
Provides an alternative to delaying the application of redo to protect against user errors or logical corruptions. Therefore, standby databases can be more closely synchronized with the primary database, thus reducing failover and switchover times.
Avoids the need to completely re-create the original primary database after a failover. The failed primary database can be flashed back to a point in time before the failover and converted to be a standby database for the new primary database.
（闪回数据库功能可快速从逻辑数据损坏和用户错误中恢复。通过允许您及时刷新，以前版本的可能被错误更改或删除的业务信息可以再次访问。此功能：
消除了恢复备份的需要，并向前滚动更改错误或损坏的时间。相反，闪回数据库可以将Oracle数据库回滚到以前的时间点，而无需还原数据文件。
提供延迟重做应用的选择，以防止用户错误或逻辑损坏。因此，备用数据库可以与主数据库更紧密地同步，从而减少故障切换和切换时间。
避免在故障转移后需要完全重新创建原始主数据库。发生故障的主数据库可以在故障转移之前闪回到某个时间点，并转换为新的主数据库的备用数据库。）
RMAN is an Oracle utility that simplifies backing up, restoring, and recovering database files. Like Data Guard, RMAN is a feature of the Oracle database and does not require separate installation. Data Guard is well integrated with RMAN, allowing you to:
Use the Recovery Manager DUPLICATE command to create a standby database from backups of your primary database.
Take backups on a physical standby database instead of the production database, relieving the load on the production database and enabling efficient use of system resources on the standby site. Moreover, backups can be taken while the physical standby database is applying redo.
Help manage archived redo log files by automatically deleting the archived redo log files used for input after performing a backup.
（RMAN是一个Oracle实用程序，可简化数据库文件的备份，恢复和恢复。与Data Guard类似，RMAN是Oracle数据库的一项功能，不需要单独安装。Data Guard与RMAN很好地集成，允许您：
使用Recovery Manager DUPLICATE命令从主数据库的备份创建备用数据库
在物理备用数据库（而不是生产数据库）上执行备份，减轻生产数据库的负载并在备用站点上高效使用系统资源。而且，可以在物理备用数据库应用重做时进行备份。
通过在执行备份后自动删除用于输入的归档重做日志文件，帮助管理归档重做日志文件。）
1.7 Summary of Data Guard Benefits
Data Guard offers these benefits:
Disaster recovery, data protection, and high availability
Data Guard provides an efficient and comprehensive disaster recovery and high availability solution. Easy-to-manage switchover and failover capabilities allow role reversals between primary and standby databases, minimizing the downtime of the primary database for planned and unplanned outages.
（Data Guard提供高效，全面的灾难恢复和高可用性解决方案。易于管理的切换和故障转移功能允许在主数据库和备用数据库之间进行角色转换，从而最大限度地减少计划内和计划外停机时主数据库的停机时间。）
Complete data protection
Data Guard can ensure zero data loss, even in the face of unforeseen disasters. A standby database provides a safeguard against data corruption and user errors. Because the redo data received from a primary database is validated at a standby database, storage level physical corruptions on the primary database do not propagate to the standby database. Similarly, logical corruptions or user errors that cause the primary database to be permanently damaged can be resolved.
（即使遇到不可预见的灾难，Data Guard也可以确保零数据丢失。备用数据库提供防止数据损坏和用户错误的安全措施。因为从主数据库接收到的重做数据在备用数据库上进行验证，所以主数据库上的存储级物理损坏不会传播到备用数据库。同样，可以解决导致主数据库永久损坏的逻辑损坏或用户错误。）
Efficient use of system resources
The standby database tables that are updated with redo data received from the primary database can be used for other tasks such as backups, reporting, summations, and queries, thereby reducing the primary database workload necessary to perform these tasks, saving valuable CPU and I/O cycles.
（该 使用从主数据库接收的重做数据更新的备用数据库表可以用于其他任务，例如 备份，报告，求和和查询，从而减少执行这些任务所需的主数据库工作负载，节省宝贵的CPU和I / O周期。）
Flexibility in data protection to balance availability against performance requirements
Oracle Data Guard offers maximum protection, maximum availability, and maximum performance modes to help enterprises balance data availability against system performance requirements.
（Oracle Data Guard提供最大限度的保护，最大可用性和最高性能模式，帮助企业实现平衡 数据可用性与系统性能要求。）
Automatic gap detection and resolution
If connectivity is lost between the primary and one or more standby databases (for example, due to network problems), redo data being generated on the primary database cannot be sent to those standby databases. Once a connection is reestablished, the missing archived redo log files (referred to as a gap) are automatically detected by Data Guard, which then automatically transmits the missing archived redo log files to the standby databases. The standby databases are synchronized with the primary database, without manual intervention by the DBA.
（如果主数据库和一个或多个备用数据库之间的连接丢失（例如，由于网络问题），主数据库上生成的重做数据将无法发送到这些备用数据库。一旦连接重新建立，缺少归档重做日志文件（称为缺口）由Data Guard自动检测，然后Data Guard自动将缺少的归档重做日志文件传输到备用数据库。备用数据库与主数据库同步，无需DBA手动干预。）
Centralized and simple management
The Data Guard broker provides a graphical user interface and a command-line interface to automate management and operational tasks across multiple databases in a Data Guard configuration. The broker also monitors all of the systems within a single Data Guard configuration.
（Data Guard经纪人提供了一个 图形用户界面和命令行界面，以便在Data Guard配置中跨多个数据库自动执行管理和操作任务。代理还监视单个Data Guard配置中的所有系统。）
Integration with Oracle Database
Data Guard is a feature of Oracle Database Enterprise Edition and does not require separate installation.
（Data Guard是Oracle数据库企业版的一项功能，不需要单独安装。）
Automatic role transitions
When fast-start failover is enabled, the Data Guard broker automatically fails over to a synchronized standby site in the event of a disaster at the primary site, requiring no intervention by the DBA. In addition, applications are automatically notified of the role transition.
（启用快速启动故障切换时，如果主站点发生灾难，Data Guard代理会自动故障转移到同步的备用站点，无需DBA干预。另外，应用程序会自动通知角色转换。）