请教关于RMAN配置问题，谢谢！
RMAN> show all;

RMAN 配置参数为:
CONFIGURE RETENTION POLICY TO REDUNDANCY 1; # default
CONFIGURE BACKUP OPTIMIZATION ON;
CONFIGURE DEFAULT DEVICE TYPE TO DISK;
CONFIGURE CONTROLFILE AUTOBACKUP OFF; # default
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE SBT_TAPE TO '%F'; # defa
ult
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '%F'; # default
CONFIGURE DEVICE TYPE 'SBT_TAPE' PARALLELISM 3 BACKUP TYPE TO BACKUPSET;
CONFIGURE DEVICE TYPE DISK PARALLELISM 3 BACKUP TYPE TO BACKUPSET;
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE SBT_TAPE TO 1; # default
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE SBT_TAPE TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE CHANNEL DEVICE TYPE DISK FORMAT 'e:\oracle_backup\%d_%s.bak';
CONFIGURE MAXSETSIZE TO 30 G;
CONFIGURE ENCRYPTION FOR DATABASE OFF; # default
CONFIGURE ENCRYPTION ALGORITHM 'AES128'; # default
CONFIGURE ARCHIVELOG DELETION POLICY TO NONE; # default
CONFIGURE SNAPSHOT CONTROLFILE NAME TO 'E:\ORACLE\PRODUCT\10.2.0\DB_1\DATABASE\SNCFDEMO.ORA'; # default
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大家好，我的RMAN 配置如上，已经配置默认设备为disk。但为何我执行
crosscheck backup或delete expired backup或delete backupset 176或 restore database
等都会提示以下的错误：
ORA-19554: 配置设备时出错, 设备类型: SBT_TAPE, 设备名称:
ORA-27211: 未能加载介质管理库

------解决方案--------------------
CONFIGURE CHANNEL DEVICE TYPE 'SBT_TAPE' clear;
------解决方案--------------------
你是要将device type为sbt_tape的backup set删除是吧
rman>allocate channel for maintenance device type sbt_tape;
rman>delete obsolete;
再试一下.