Differential Incremental Backups 和Cumulative Incremental Backups

差异与累计增量备份

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本文介绍了数据库备份中两种重要的增量备份策略：差异增量备份和累计增量备份。差异增量备份记录自最近一次相同级别的备份以来更改的所有块，而累计增量备份则备份自最近一次0级备份以来使用的所有块。累计备份虽然简化了恢复过程，但占用更多存储空间。

Differential Incremental Backups

In a differential level 1 backup, RMAN backs up all blocks that have changed since the most recent incremental backup at level 1 (cumulative or differential) or level 0. For example, in a differential level 1 backup, RMAN determines which level 1 backup occurred most recently and backs up all blocks modified after that backup. If no level 1 is available, RMAN copies all blocks changed since the base level 0 backup.

If no level 0 backup is available, then the behavior varies with the compatibility mode setting. If compatibility is >=10.0.0, RMAN copies all blocks that have been changed since the file was created. Otherwise, RMAN behaves as it did in previous releases, by generating a level 0 backup.

Figure 2-4 Differential Incremental Backups

Description of "Figure 2-4 Differential Incremental Backups"

In the example shown in Figure 2-4 , the following occurs each week:

Sunday

An incremental level 0 backup backs up all blocks that have ever been in use in this database.
Monday - Saturday

On each day from Monday through Saturday, a differential incremental level 1 backup backs up all blocks that have changed since the most recent incremental backup at level 1 or 0. The Monday backup copies blocks changed since Sunday level 0 backup, the Tuesday backup copies blocks changed since the Monday level 1 backup, and so forth.

Cumulative Incremental Backups

In a cumulative level 1 backup, RMAN backs up all the blocks used since the most recent level 0 incremental backup. Cumulative incremental backups reduce the work needed for a restore by ensuring that you only need one incremental backup from any particular level. Cumulative backups require more space and time than differential backups, however, because they duplicate the work done by previous backups at the same level.

Figure 2-5 Cumulative Incremental Backups

Description of "Figure 2-5 Cumulative Incremental Backups"

In the example shown in Figure 2-5 , the following occurs each week:

Sunday

An incremental level 0 backup backs up all blocks that have ever been in use in this database.
Monday - Saturday

A cumulative incremental level 1 backup copies all blocks changed since the most recent level 0 backup. Because the most recent level 0 backup was created on Sunday, the level 1 backup on each day Monday through Saturday backs up all blocks changed since the Sunday backup.