Oracle Database Backup and Recovery Reference【每日一译】--2012-11-12

RMAN can also store backup information a logical structure called a backup set. A
backup set contains the data from one or more datafiles, archived redo logs, or control
files or SPFILE. (Datafiles and archivelogs cannot be mixed together in the same

backup set.) You can also back up existing backup sets into another backup set.

RMAN也可以存储备份信息在一个逻辑结构叫作备份集合。一个备份集合包含了一个或

多个数据文件，归档重做日志，或者控制文件或者SPFILE.（数据文件和归档日志不能混在

同一个备份集中）你也可以将已存在的备份集备份到另一个备份集。

A backup set consists of one or more files in an RMAN-specific format, known as
backup pieces. By default, a backup set consists of one backup piece. For example,
you can back up ten datafiles into a single backup set consisting of a single backup
piece (that is, one backup piece will be produced as output, the backup set consists of
the single file containing the backup piece, and the backup piece and the backup set
that contains it will be recorded in the RMAN repository). A file cannot be split across
backup sets.

一个备份集在RMAN-指定格式中由一个或者多个文件组成，众所知道的备份片。默认的一个

备份集由一个备份片组成。比如，你可以备份10个文件到一个由单独备份片构成的备份集，

（也就是，一个备份片作为输出创建，备份集由一个包含备份片的单独文件构成，并且备份

片和包含备份片的备份集它们将记录在RMAN的仓库里）。一个文件不能通过备份集将它分离。

Note: The backup set is the smallest unit of a backup. RMAN only
records backup sets in the repository that complete successfully.
There is no such thing as a partial backup set. You cannot usefully
manipulate individual backup pieces.

备注：备份集是最小的备份单元。RMAN只记录备份集到仓库里，并且它们都是完全成功的。

没有包含部分备份集的东西。你不能有效的操作单独的备份片。

Only RMAN can create or restore from backup sets. When multiple files are backed up
into the same backup set, they are read concurrently and their data is multiplexed
together.

只有RMAN可以从备份集中创建或者修复。当多个文件备份到一个相同的备份集，它们被

并发读取并且它们数据是多份复制一起。

Backup sets are the only type of backup that RMAN supports on media manager
devices such as tapes. Backup sets can also be created on disk. By default, RMAN
creates backups both on both disk and on tape as backup sets.

备份集是仅有的备份类型，它是RMAN支持的介质管理设备比如磁带所支持的。备份集

也可以创建在磁盘上。默认的，RMAN创建同时在磁盘和磁带上作为备份集备份。

When backing up datafiles to backup sets, RMAN is able to skip some datafile blocks
that do not currently contain data, reducing the size of backup sets and the time
required to create them. This behavior, known as unused block compression, means
that backups of datafiles as backup sets are generally smaller than image copy backups
and take less time to write. This behavior is fundamental to how RMAN writes
datafiles into backup pieces, and cannot be disabled. For more information about how
and when unused blocks are skipped, see Oracle Database Backup and Recovery
Reference.

当备份数据文件到备份集，RMAN可以跳过一些文件块（它不是当前包含的数据),减少备份

集的大小和创建备份的时间。这种行为就是所知的UNUSED BLOCK COMPRESSION,也意

味着作为备份集的数据文件的备份一般小于镜像COPY备份并且在写入上花费更少的时间。

这种行为它是RMAN如何将数据文件写入到备份片的基础，并且不能被禁止。需获取更多关于

如何跳过UNUSED BLOCKS信息，也可查看Oracle Database Backup and Recovery
Reference.

RMAN also supports binary compression of backup sets, where the backup set
contents are compressed before being written to disk using a compression algorithm
tuned for compression of datafiles and archived log files.

RMAN也支持二进制的备份集压缩，在那里备份集的内容在写入磁盘前被压缩采用一个压缩算法

调试对于数据文件和归档日志文件的压缩。