1.使用快照先决条件：主备库开启闪回功能
2.把备库转为快照库
DGMGRL> convert database satest to SNAPSHOT STANDBY; Converting database "satest" to a Snapshot Standby database, please wait... Database "satest" converted successfully
3.把快照库转回物理备库
DGMGRL> convert database satest to PHYSICAL STANDBY; Converting database "satest" to a Physical Standby database, please wait... Operation requires shutdown of instance "atest" on database "satest" Shutting down instance "atest"... Database closed. Database dismounted. ORACLE instance shut down. Operation requires startup of instance "atest" on database "satest" Starting instance "atest"... ORA-32004: obsolete or deprecated parameter(s) specified for RDBMS instance ORACLE instance started. Database mounted. Continuing to convert database "satest" ... Operation requires shutdown of instance "atest" on database "satest" Shutting down instance "atest"... ORA-01109: database not open Database dismounted. ORACLE instance shut down. Operation requires startup of instance "atest" on database "satest" Starting instance "atest"... ORA-32004: obsolete or deprecated parameter(s) specified for RDBMS instance ORACLE instance started. Database mounted. Database "satest" converted successfully
4.小结：
a.备库处于快照期间，主库的日志不能丢失，否则快照库无法恢复为物理备库
b.快照库允许做任何操作，当恢复到物理备库时，所有对快照库做的操作都将会滚
C.个人建议，有两个及以上备库的架构合适使用快照库，只有一个备库时，谨慎使用.