backup命令可以创建备份集或者镜像拷贝两种备份类型。在磁盘上，
我们可以备份为备份集或者镜像拷贝。默认的备份类型是未压缩的备份集。在磁盘上，备份类型只能是备份集，不能设置为镜像拷贝。
配置默认备份类型
1.默认镜像文件到磁盘
CONFIGURE DEVICE TYPE DISK BACKUP TYPE TO COPY;
2.默认备份集到磁盘
CONFIGURE DEVICE TYPE DISK BACKUP TYPE TO BACKUPSET;
3.默认压缩备份集到磁盘
CONFIGURE DEVICE TYPE DISK BACKUP TYPE TO COMPRESSED BACKUPSET;
4.默认压缩备份集到磁带
CONFIGURE DEVICE TYPE sbt BACKUP TYPE TO COMPRESSED BACKUPSET;
尝试更改默认配置为镜像拷贝到磁盘
RMAN> show device type;
RMAN configuration parameters for database with db_unique_name TEST are:
CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET; # default
RMAN> CONFIGURE DEVICE TYPE DISK BACKUP TYPE TO COPY;
new RMAN configuration parameters:
CONFIGURE DEVICE TYPE DISK BACKUP TYPE TO COPY PARALLELISM 1;
new RMAN configuration parameters are successfully stored
released channel: ORA_DISK_1
RMAN> show device type;
RMAN configuration parameters for database with db_unique_name TEST are:
CONFIGURE DEVICE TYPE DISK BACKUP TYPE TO COPY PARALLELISM 1;
尝试更改默认配置为镜像拷贝到磁带
RMAN> CONFIGURE DEVICE TYPE sbt BACKUP TYPE TO COPY;
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of configure command at 07/23/2017 22:50:47
RMAN-06609: AS COPY can be configured only for disk device
失败
更改默认配置为备份集到磁带
RMAN> CONFIGURE DEVICE TYPE sbt BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters:
CONFIGURE DEVICE TYPE 'SBT_TAPE' BACKUP TYPE TO BACKUPSET PARALLELISM 1;
new RMAN configuration parameters are successfully stored
RMAN> configure default device type to sbt;
old RMAN configuration parameters:
CONFIGURE DEFAULT DEVICE TYPE TO 'SBT_TAPE';
new RMAN configuration parameters:
CONFIGURE DEFAULT DEVICE TYPE TO 'SBT_TAPE';
new RMAN configuration parameters are successfully stored
两个语句都修改成功，配置默认备份设备的语句 configure default device type to xxx其实指定了默认备份类型为非压缩型的备份集。
