今天导数据时报错，发现提示有类似权限的错误，但是修改过权限后还是一直的报错，搜了一下有网友也遇到同样的错误
不过可能是我的rac环境只开启了一个节点，可能跟 cluster集群的有关系
刚开始一度怀疑是dir_dp的物理目录权限不够
给了775权限
但是还不行
官方文档这样写道
UsingPARALLEL During An Export In An Oracle RAC Environment
In an Oracle Real Application Clusters(Oracle RAC) environment, if an export operation has PARALLEL=1, then all Data Pump processes reside on the instance where the job isstarted. Therefore, the directory object can point to local storage for thatinstance.
If the export operation has PARALLEL set to a value greater than 1, then Data Pump processes can resideon instances other than the one where the job was started. Therefore, the directoryobject must point to shared storage that is accessible by all instances of theOracle RAC.
看来是导出文件的目录不是两个节点共享的原因，/backup只在节点1上挂载，节点2上没有。如果/backup在两个节点共享，就不会出现这样的错误。但是现在只能在单实例上操作。查看expdp的help，发现有个参数cluster。这个参数可以控制是否采用多实例导出。设置cluster=n后，即：
expdp system/system directory=backup dumpfile=db_full.dump cluster=n logfile=db_full_20180307.log parallel=8
执行后导出正常。没有报错
