一 问题描述
客户说RMAN备份脚本执行有的时候报错，有的时候正常！！！
远程登陆客户环境，查询最后一次备份的日志报错信息，得到
RMAN-03002: failure of delete command at xxx
RMAN-06091: no channel allocated for maintenance (of an appropriate type)
二 参考链接
https://www.linuxidc.com/Linux/2013-01/78144.htm
Encountered RMAN-03002 and RMAN-06091 when Deleting Obsolete Backups (文档 ID 567555.1)
根据上述信息，可以得到问题的原因，一般再删除过期的备份脚本时，如果通道默认都是disk磁盘，如果存在sbt磁带备份，则无法通过这个通道删除它，因此需要转换一下。
SOLUTION
To implement the solution, please execute the following steps: Please run the following commands to delete obsolete backup sets on both disk and tape: RMAN> allocate channel for maintenance type disk;
RMAN> allocate channel for maintenance device type 'sbt_tape' PARMS '...';
==>Please contact your MML(Media Management Layer) vendor to get the actual tape parameters and repalce the '...' . RMAN> delete obsolete; If you want to delete obsolete backup sets on disk, you can use the following commands:
RMAN> allocate channel for maintenance type disk;
RMAN> delete obsolete device type disk;