8.8.1 About Multilevel Incremental Backups
RMAN can create multilevel incremental backups. Each incremental level is denoted by a value of 0 or 1.
RMAN有多级增量备份，增量级别由0或1的值表示。
A level 0 incremental backup, which is the base for subsequent incremental backups, copies all blocks containing data. The only difference between a level 0 incremental backup and a full backup is that a full backup is never included in an incremental strategy. Thus, an incremental level 0 backup is a full backup that happens to be the parent of incremental backups whose level is greater than 0.
0级别的增量备份，后续备份的基础，需要复制所有的数据块包含的数据。0级别的备份和全量备份唯一的不同是全量备份没有增量策略。所以说，增量0级备份是完全备份，它恰好是级别大于0的增量备份的父级。
A level 1 incremental backup can be either of the following types:
A differential incremental backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
差异增量备份，将会备份从最近的级别0或级别1备份后所有改变的数据块
A cumulative incremental backup, which backs up all blocks changed after the most recent incremental backup at level 0
累积增量备份，备份在0级最近一次增量备份之后更改的所有块。（不怎么清楚他备份后会不会删除之前备份的1级备份）
Incremental backups are differential by default.
增量备份的默认方式是differential的。
Incremental backups at level 0 can be either backup sets or image copies, but incremental backups at level 1 can only be backup sets.
0级的增量备份可以是备份集或映像副本，但1级的增量备份只能是备份集。
