备份设备 (SQL Server)Backup Devices (SQL Server)

适用对象:是SQL Server 否Azure SQL 数据库 否Azure Synapse Analytics (SQL DW) 否并行数据仓库APPLIES TO: yesSQL Server noAzure SQL Database noAzure Synapse Analytics (SQL DW) noParallel Data Warehouse

SQL ServerSQL Server 数据库上执行备份操作期间,将备份的数据(“备份” )写入物理备份设备。During a backup operation on a SQL ServerSQL Server database, the backed up data (the backup) is written to a physical backup device. 将介质集中的第一个备份写入物理备份设备时,便会初始化此备份设备。This physical backup device is initialized when the first backup in a media set is written to it. 包含一个或多个备份设备的集合的备份构成一个媒体集。Backups on a set of one or more backup devices compose a single media set.

术语和定义Terms and definitions

备份磁盘 (backup disk)backup disk
包含一个或多个备份文件的硬盘或其他磁盘存储介质。A hard disk or other disk storage media that contains one or more backup files. 备份文件是常规操作系统文件。A backup file is a regular operating system file.

介质集 (media set)media set
备份介质(磁带或磁盘文件)的有序集合,它使用固定类型和数量的备份设备。An ordered collection of backup media, tapes or disk files, that uses a fixed type and number of backup devices. 有关媒体集的信息,请参阅 媒体集、媒体簇和备份集 (SQL Server)For more information about media sets, see Media Sets, Media Families, and Backup Sets (SQL Server).

物理备份设备 (physical backup device)physical backup device
磁带机或操作系统提供的磁盘文件。Either a tape drive or a disk file that is provided by the operating system. 可以将备份数据写入 1 到 64 个备份设备。A backup can be written to from 1 to 64 backup devices. 如果备份数据需要多个备份设备,则所有设备必须对应于一种设备类型(磁盘或磁带)。If a backup requires multiple backup devices, the devices all must correspond to a single type of device (disk or tape).

除了磁盘或磁带外,还可以将 SQL Server 备份写入 Azure Blob 存储服务。SQL Server Backups can also be written to Azure Blob storage service in addition to disk or tape.

使用磁盘备份设备Using disk backup devices

如果在备份操作将备份数据追加到介质集时磁盘文件已满,则备份操作会失败。If a disk file fills while a backup operation is appending a backup to the media set, the backup operation fails. 备份文件的最大大小由磁盘设备上的可用磁盘空间决定,因此,备份磁盘设备的适当大小取决于备份数据的大小。The maximum size of a backup file is determined by the free disk space available on the disk device; therefore, the appropriate size for a backup disk device depends on the size of your backups.

磁盘备份设备可以是简单的磁盘设备,如 ATA 驱动器。A disk backup device could be a simple disk device, such as an ATA drive. 或者,您可以使用热交换磁盘驱动器,它允许您将驱动器上的已满磁盘透明地替换为空磁盘。Alternatively, you could use a hot-swappable disk drive that would let you transparently replace a full disk on the drive with an empty disk. 备份磁盘可以是服务器上的本地磁盘,也可以是作为共享网络资源的远程磁盘。A backup disk can be a local disk on the server or a remote disk that is a shared network resource. 有关如何使用远程磁盘的信息,请参阅本主题后面的 备份到网络共享文件For information about how to use a remote disk, see Backing Up to a File on a Network Share, later in this topic.

SQL ServerSQL Server 管理工具在处理磁盘备份设备时非常灵活,因为它们会自动生成标有时间戳的磁盘文件名称。management tools are very flexible at handling disk backup devices because they automatically generate a time-stamped name on the disk file.

重要说明!IMPORTANT! 我们建议备份磁盘应不同于数据库数据和日志的磁盘。We recommend that a backup disk be a different disk than the database data and log disks. 这是数据或日志磁盘出现故障时访问备份数据必不可少的。This is necessary to make sure that you can access the backups if the data or log disk fails.

如果数据库文件和备份文件位于同一台设备上并且该设备出现故障,数据库和备份都将不可用。If database files and backup files are on the same device and the device fails, the database and backups will be unavailable. 此外,将数据库和备份文件放到不同的设备上还可以优化使用数据库和写入备份时的 I/O 性能。Also, putting the database and backup files on the separate devices optimizes the I/O performance for both the production use of the database and the writing of backups.

使用物理名称指定备份文件 (Transact-SQL)Specify a backup file using its physical name (Transact-SQL)

使用物理设备名称指定备份文件的基本 BACKUP 语法为:The basic BACKUP syntax for specifying a backup file by using its physical device name is:

BACKUP DATABASE database_nameBACKUP DATABASE database_name

TO DISK = { ' physical_backup_device_name ' | @ physical_backup_device_name_var }TO DISK = { 'physical_backup_device_name' | @physical_backup_device_name_var }

例如:For example:

BACKUP DATABASE AdventureWorks2012   
   TO DISK = 'Z:\SQLServerBackups\AdventureWorks2012.bak';  
GO  

若要在 RESTORE 语句中指定物理磁盘设备,基本语法为:To specify a physical disk device in a RESTORE statement, the basic syntax is:

RESTORE { DATABASE | LOG } database_nameRESTORE { DATABASE | LOG } database_name

FROM DISK = { ' physical_backup_device_name ' | @ physical_backup_device_name_var }FROM DISK = { 'physical_backup_device_name' | @physical_backup_device_name_var }

例如,For example,

RESTORE DATABASE AdventureWorks2012   
   FROM DISK = 'Z:\SQLServerBackups\AdventureWorks2012.bak';   

指定磁盘备份文件路径Specify the disk backup file path

指定备份文件时,应输入其完整路径和文件名。When you are specifying a backup file, you should enter its full path and file name. 如果您在备份到文件时仅指定文件名或相对路径,则备份文件将存储到默认备份目录中。If you specify only the file name or a relative path when you are backing up to a file, the backup file is put in the default backup directory. 默认备份目录为 C:\Program Files\Microsoft SQL Server\MSSQL.n\MSSQL\Backup,其中 n 是服务器实例号。The default backup directory is C:\Program Files\Microsoft SQL Server\MSSQL.n\MSSQL\Backup, where n is the number of the server instance. 因此,对于默认服务器实例,默认备份目录为:C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\Backup。Therefore, for the default server instance, the default backup directory is: C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\Backup.

为防止产生歧义,尤其是在脚本中,我们建议您在每个 DISK 子句中显式指定备份目录的路径。To avoid ambiguity, especially in scripts, we recommend that you explicitly specify the path of the backup directory in every DISK clause. 但是,当您使用查询编辑器时这一点不再那么重要。However, this is less important when you are using Query Editor. 此时,如果您确定备份文件位于默认备份目录中,则可以省略 DISK 子句中的路径。In that case, if you are sure that the backup file resides in the default backup directory, you can omit the path from a DISK clause. 例如,下面的 BACKUP 语句将 AdventureWorks2012AdventureWorks2012 数据库备份到默认的备份目录中。For example, the following BACKUP statement backs up the AdventureWorks2012AdventureWorks2012 database to the default backup directory.

BACKUP DATABASE AdventureWorks2012   
   TO DISK = 'AdventureWorks2012.bak';  
GO  

注意: 默认位置存储在 HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL.n\MSSQLServer 下的 BackupDirectory注册表项中。NOTE: The default location is stored in the BackupDirectory registry key under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL.n\MSSQLServer.

备份到网络共享文件Back up to a network share file

要让 SQL ServerSQL Server 访问远程磁盘文件, SQL ServerSQL Server 服务帐户必须有权访问网络共享。For SQL ServerSQL Server to access a remote disk file, the SQL ServerSQL Server service account must have access to the network share. 这包括备份操作向网络共享中写入所需的权限以及还原操作从网络共享中读取所需的权限。This includes having the permissions needed for backup operations to write to the network share and for restore operations to read from it. 网络驱动器和权限的可用性取决于 SQL ServerSQL Server 服务运行的环境:The availability of network drives and permissions depends on the context is which SQL ServerSQL Server service is running:

  • 若要在 SQL ServerSQL Server 使用域用户帐户运行时备份到网络驱动器,共享驱动器必须在 SQL ServerSQL Server 运行的会话中作为网络驱动器进行映射。To back up to a network drive when SQL ServerSQL Server is running in a domain user account, the shared drive must be mapped as a network drive in the session where SQL ServerSQL Server is running. 如果是通过命令行启动 Sqlservr.exe 的,则 SQL ServerSQL Server 可以看到在登录会话中映射的所有网络驱动器。If you start Sqlservr.exe from command line, SQL ServerSQL Server sees any network drives you have mapped in your login session.

  • 作为服务运行 Sqlservr.exe 时, SQL ServerSQL Server 将在单独的会话中运行,该会话与登录会话无关。When you run Sqlservr.exe as a service, SQL ServerSQL Server runs in a separate session that has no relation to your login session. 运行服务的会话可以具有自己的映射驱动器(虽然它一般没有映射驱动器)。The session in which a service runs can have its own mapped drives, although it usually does not.

  • 可以使用计算机帐户(而不是域用户)连接网络服务帐户。You can connect with the network service account by using the computer account instead of a domain user. 若要允许从特定计算机备份到共享驱动器,请向计算机帐户授予访问权限。To enable backups from specific computers to a shared drive, grant access to the computer accounts. 只要写入备份的 Sqlservr.exe 进程具有访问权限,那么发送 BACKUP 命令的用户是否具有访问权限便会无关紧要。As long as the Sqlservr.exe process that is writing the backup has access, it is irrelevant whether the user sending the BACKUP command has access.

    重要说明!IMPORTANT! 在网络上备份数据可能受网络错误的影响;因此,建议在使用远程磁盘时,完成备份后验证备份操作。Backing up data over a network can be subject to network errors; therefore, we recommend that when you are using a remote disk you verify the backup operation after it finishes. 有关详细信息,请参阅 RESTORE VERIFYONLY (Transact-SQL)For more information, see RESTORE VERIFYONLY (Transact-SQL).

指定通用命名约定 (UNC) 名称Specify a Universal Naming Convention (UNC) name

若要在备份或还原命令中指定网络共享,应针对备份设备使用文件的完全限定通用命名约定 (UNC) 名称。To specify a network share in a backup or restore command, use the fully qualified universal naming convention (UNC) name of the file for the backup device. UNC 名称采用以下格式: \\ 系统名称 \ 共享名称 \ 路径 \ 文件名A UNC name has the form \\Systemname\ShareName\Path\FileName.

例如:For example:

BACKUP DATABASE AdventureWorks2012   
   TO DISK = '\\BackupSystem\BackupDisk1\AW_backups\AdventureWorksData.Bak';  
GO  

使用磁带设备Using tape devices

注意:SQL ServerSQL Server的未来版本中将不再支持磁带备份设备。NOTE: Support for tape backup devices will be removed in a future version of SQL ServerSQL Server. 请避免在新的开发工作中使用该功能,并着手修改当前还在使用该功能的应用程序。Avoid using this feature in new development work, and plan to modify applications that currently use this feature.

SQL ServerSQL Server 数据备份到磁带时要求 MicrosoftMicrosoft Windows 操作系统支持一个或多个磁带机。Backing up SQL ServerSQL Server data to tape requires that the tape drive or drives be supported by the MicrosoftMicrosoft Windows operating system. 另外,对于给定的磁带机,我们建议您仅使用磁带机制造商推荐的磁带。Additionally, for the given tape drive, we recommend that you use only tapes recommended by the drive manufacturer. 有关如何安装磁带机的详细信息,请参阅 Windows 操作系统的文档。For more information about how to install a tape drive, see the documentation for the Windows operating system.

在使用磁带机时,备份操作可能会写满一个磁带,并继续在另一个磁带上进行。When a tape drive is used, a backup operation may fill one tape and continue onto another tape. 每个磁带包含一个介质标头。Each tape contains a media header. 使用的第一个介质称为“起始磁带 ”。The first media used is called the initial tape. 每个后续磁带称为“延续磁带” ,其介质序列号比前一磁带的介质序列号大一。Each successive tape is known as a continuation tape and has a media sequence number that is one higher than the previous tape. 例如,与四个磁带设备相关联的介质集至少含有四个起始磁带(如果该数据库过大,还会有四个系列的延续磁带)。For example, a media set associated with four tape devices contains at least four initial tapes (and, if the database does not fit, four series of continuation tapes). 在追加备份集时,必须在序列中装入最后一个磁带。When appending a backup set, you must mount the last tape in the series. 如果没有装入最后一个磁带, 数据库引擎Database Engine 将向前扫描到已装入磁带的末尾,然后要求更换磁带。If the last tape is not mounted, the 数据库引擎Database Engine scans forward to the end of the mounted tape and then requires that you change the tape. 此时,请装入最后一个磁带。At that point, mount the last tape.

磁带备份设备的用法类似于磁盘设备,但下述情况例外:Tape backup devices are used like disk devices, with the following exceptions:

  • 磁带设备必须物理连接到运行 SQL ServerSQL Server实例的计算机上。The tape device must be connected physically to the computer that is running an instance of SQL ServerSQL Server. 不支持备份到远程磁带设备上。Backing up to remote tape devices is not supported.

  • 如果磁带备份设备在备份操作过程中已满,但还必须写入一些数据,则 SQL ServerSQL Server 将提示更换新磁带并在加载新磁带后继续备份操作。If a tape backup device is filled during the backup operation, but more data still must be written, SQL ServerSQL Server prompts for a new tape and continues the backup operation after a new tape is loaded.

使用物理名称指定备份磁带 (Transact-SQL)Specify a backup tape using its physical name (Transact-SQL)

使用磁带机物理设备名称指定备份磁带的基本 BACKUP 语法为:The basic BACKUP syntax for specifying a backup tape using the physical device name of the tape drive is:

BACKUP { DATABASE | LOG } database_nameBACKUP { DATABASE | LOG } database_name

TO TAPE = { ' physical_backup_device_name ' | @ physical_backup_device_name_var }TO TAPE = { 'physical_backup_device_name' | @physical_backup_device_name_var }

例如:For example:

BACKUP LOG AdventureWorks2012   
   TO TAPE = '\\.\tape0';  
GO  

若要在 RESTORE 语句中指定物理磁带设备,基本语法为:To specify a physical tape device in a RESTORE statement, the basic syntax is:

RESTORE { DATABASE | LOG } database_nameRESTORE { DATABASE | LOG } database_name

FROM TAPE = { ' physical_backup_device_name ' | @ physical_backup_device_name_var }FROM TAPE = { 'physical_backup_device_name' | @physical_backup_device_name_var }

磁带专用的 BACKUP 选项和 RESTORE 选项 (Transact-SQL)Tape-Specific BACKUP and RESTORE options (Transact-SQL)

为了便于磁带管理,BACKUP 语句提供了下列磁带专用的选项:To facilitate tape management, the BACKUP statement provides the following tape-specific options:

  • { NOUNLOAD | UNLOAD }{ NOUNLOAD | UNLOAD }

    您可以控制在备份或还原操作后备份磁带是否自动从磁带机卸载。You can control whether a backup tape is unloaded automatically from the tape drive after a backup or restore operation. UNLOAD/NOUNLOAD 这一会话设置可在整个会话期间存在,或者在通过指定其他设置而进行重置之前一直存在。UNLOAD/NOUNLOAD is a session setting that persists for the life of the session or until it is reset by specifying the alternative.

  • { REWIND | NOREWIND }{ REWIND | NOREWIND }

    您可以控制在备份或还原操作后 SQL ServerSQL Server 是保持磁带处于打开状态,还是在磁带满后释放磁带并倒带。You can control whether SQL ServerSQL Server keeps the tape remains open after the backup or restore operation or releases and rewinds the tape after it fills. 默认行为是倒带 (REWIND)。The default behavior is to rewind the tape (REWIND).

注意: 有关 BACKUP 语法和参数的详细信息,请参阅 BACKUP (Transact-SQL)NOTE: For more information about the BACKUP syntax and arguments, see BACKUP (Transact-SQL). 有关 RESTORE 语法和参数的详细信息,请分别参阅 RESTORE (Transact-SQL)RESTORE 参数 (Transact-SQL)For more information about the RESTORE syntax and arguments, see RESTORE (Transact-SQL) and RESTORE Arguments (Transact-SQL), respectively.

管理打开的磁带Managing open tapes

若要查看打开的磁带设备列表以及装入请求状态,请查询 sys.dm_io_backup_tapes 动态管理视图。To view a list of open tape devices and the status of mount requests, query the sys.dm_io_backup_tapes dynamic management view. 此视图显示了所有打开的磁带。This view shows all the open tapes. 其中包括正在使用的磁带,它们等待下一个 BACKUP 或 RESTORE 操作时暂时处于空闲状态。These include in-use tapes that are temporarily idle while they wait for the next BACKUP or RESTORE operation.

如果意外使磁带处于打开状态,则释放磁带的最快方式是使用以下命令:RESTORE REWINDONLY FROM TAPE = backup_device_nameIf a tape has been accidentally left open, the fastest way to release the tape is by using the following command: RESTORE REWINDONLY FROM TAPE =backup_device_name. 有关详细信息,请参阅 RESTORE REWINDONLY (Transact-SQL)For more information, see RESTORE REWINDONLY (Transact-SQL).

使用 Azure Blob 存储服务Using the Azure Blob Storage service

可以将 SQL Server 备份写入 Azure Blob 存储服务。SQL Server Backups can be written to the Azure Blob Storage Service. 有关如何将 Azure Blob 存储服务用于你的备份的详细信息,请参阅使用 Microsoft Azure Blob 存储服务进行 SQL Server 备份和还原For more information on how to use the Azure Blob storage service for your backups, see SQL Server Backup and Restore with Microsoft Azure Blob Storage Service.

使用逻辑备份设备Use a logical backup device

“逻辑备份设备 ”是指向特定物理备份设备(磁盘文件或磁带机)的可选用户定义名称。A logical backup device is an optional, user-defined name that points to a specific physical backup device (a disk file or tape drive). 通过逻辑备份设备,您可以在引用相应的物理备份设备时使用间接寻址。A logical backup device lets you use indirection when referencing the corresponding physical backup device.

定义逻辑备份设备涉及为物理设备分配逻辑名称。Defining a logical backup device involves assigning a logical name to a physical device. 例如,逻辑设备 AdventureWorksBackups 可能被定义为指向 Z:\SQLServerBackups\AdventureWorks2012.bak 文件或 \\.\tape0 磁带驱动器。For example, a logical device, AdventureWorksBackups, could be defined to point to the Z:\SQLServerBackups\AdventureWorks2012.bak file or the \\.\tape0 tape drive. 备份和还原命令随后可以将 AdventureWorksBackups 指定为备份设备,而不是指定 DISK = 'Z:\SQLServerBackups\AdventureWorks2012.bak' 或 TAPE = '\\.\tape0'。Backup and restore commands can then specify AdventureWorksBackups as the backup device, instead of DISK = 'Z:\SQLServerBackups\AdventureWorks2012.bak' or TAPE = '\\.\tape0'.

逻辑设备名称在服务器实例上的所有逻辑备份设备中必须是唯一的。The logical device name must be unique among all the logical backup devices on the server instance. 若要查看现有逻辑设备名称,请查询 sys.backup_devices 目录视图。To view the existing logical device names, query the sys.backup_devices catalog view. 此视图显示每个逻辑备份设备的名称,并说明了相应物理备份设备的类型、物理文件名或路径。This view displays the name of each logical backup device and describes the type and physical file name or path of the corresponding physical backup device.

定义逻辑备份设备后,您可以在 BACKUP 或 RESTORE 命令中指定此逻辑备份设备而不是设备的物理名称。After a logical backup device is defined, in a BACKUP or RESTORE command, you can specify the logical backup device instead of the physical name of the device. 例如,下面的语句将 AdventureWorks2012 数据库备份到 AdventureWorksBackups 逻辑备份设备。For example, the following statement backs up the AdventureWorks2012 database to the AdventureWorksBackups logical backup device.

BACKUP DATABASE AdventureWorks2012   
   TO AdventureWorksBackups;  
GO  

注意: 在给定的 BACKUP 或 RESTORE 语句中,逻辑备份设备名称和相应的物理备份设备名称可以互换。NOTE: In a given BACKUP or RESTORE statement, the logical backup device name and the corresponding physical backup device name are interchangeable.

使用逻辑备份设备的一个优点是比使用长路径简单。One advantage of using a logical backup device is that it is simpler to use than a long path. 如果准备将一系列备份数据写入相同的路径或磁带设备,则使用逻辑备份设备非常有用。Using a logical backup device can help if you plan to write a series of backups to the same path or to a tape device. 逻辑备份设备对于标识磁带备份设备尤为有用。Logical backup devices are especially useful for identifying tape backup devices.

可以编写一个备份脚本以使用特定逻辑备份设备。A backup script can be written to use a particular logical backup device. 这样,您无需更新脚本即可切换到新的物理备份设备。This lets you switch to a new physical backup devices without updating the script. 切换涉及以下过程:Switching involves the following process:

  1. 删除原来的逻辑备份设备。Dropping the original logical backup device.

  2. 定义新的逻辑备份设备,新设备使用原来的逻辑设备名称,但映射到不同的物理备份设备。Defining a new logical backup device that uses the original logical device name but maps to a different physical backup device. 逻辑备份设备对于标识磁带备份设备尤为有用。Logical backup devices are especially useful for identifying tape backup devices.

镜像备份媒体集Mirrored backup media sets

镜像备份介质集可减小备份设备故障的影响。Mirroring of backup media sets reduces the effect of backup-device malfunctions. 由于备份是防止数据丢失的最后防线,因此备份设备出现故障的后果是非常严重的。These malfunctions are especially serious because backups are the last line of defense against data loss. 随着数据库不断增大,备份设备或介质发生故障致使备份不可还原的可能性也相应增加。As the sizes of databases grow, the probability increases that a failure of a backup device or media will make a backup nonrestorable. 镜像备份介质通过提供物理备份设备冗余来提高备份的可靠性。Mirroring backup media increases the reliability of backups by providing redundancy for the physical backup device. 有关详细信息,请参阅本主题后面的 镜像备份媒体集 (SQL Server)不熟悉的读者。For more information, see Mirrored Backup Media Sets (SQL Server).

注意: 只有 SQL Server 2005 Enterprise EditionSQL Server 2005 Enterprise Edition 和更高版本支持镜像备份介质集。NOTE: Mirrored backup media sets are supported only in SQL Server 2005 Enterprise EditionSQL Server 2005 Enterprise Edition and later versions.

存档 SQL Server 备份Archive SQL Server backups

建议您使用文件系统备份实用工具对磁盘备份数据进行存档,并将存档存储在另一个位置。We recommend that you use a file system backup utility to archive the disk backups and that you store the archives off-site. 使用磁盘的优点是您可以使用网络将已存档的备份数据写入另一个位置的磁盘。Using disk has the advantage that you use the network to write the archived backups onto an off-site disk. Azure Blob 存储服务可作为站外存档选项。The Azure Blob storage service can be used as off-site archival option. 可以上载磁盘备份,或直接将备份写入 Azure Blob 存储服务。You can either upload your disk backups, or directly write the backups to the Azure Blob storage service.

另一个常用的存档方法是将 SQL ServerSQL Server 备份写入本地备份磁盘,将备份存档到磁带,然后在将磁带存储在站外位置。Another common archiving approach is to write SQL ServerSQL Server backups onto a local backup disk, archive them to tape, and then store the tapes off-site.

Related tasksRelated tasks

指定磁盘设备 (SQL Server Management Studio)To specify a disk device (SQL Server Management Studio)

指定磁带设备 (SQL Server Management Studio)To specify a tape device (SQL Server Management Studio)

定义逻辑备份设备To define a logical backup device

使用逻辑备份设备To use a logical backup device

查看有关备份设备的信息To View Information About Backup Devices

删除逻辑备份设备To delete a logical backup device

另请参阅See also

SQL Server Backup Device 对象 SQL Server, Backup Device Object
BACKUP (Transact-SQL) BACKUP (Transact-SQL)
维护计划 Maintenance Plans
媒体集、媒体簇和备份集 (SQL Server) Media Sets, Media Families, and Backup Sets (SQL Server)
RESTORE (Transact-SQL) RESTORE (Transact-SQL)
RESTORE LABELONLY (Transact-SQL) RESTORE LABELONLY (Transact-SQL)
sys.backup_devices (Transact-SQL) sys.backup_devices (Transact-SQL)
sys.dm_io_backup_tapes (Transact-SQL) sys.dm_io_backup_tapes (Transact-SQL)
镜像备份媒体集 (SQL Server)Mirrored Backup Media Sets (SQL Server)