RMAN删除obsolete时报错：RMAN-06091

在rman中执行delete noprompt obsolete出现了如下报错：
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of delete command at 12/30/2013 13:51:36
RMAN-06091: no channel allocated for maintenance (of an appropriate type)
原因是存在其他类型的备份，需要分配维护通道再进行删除
因此命令需要加上devicetype disk：
RMAN> delete noprompt obsolete device type disk;