为备份数据库，通过NFS的方式，在数据库上挂载了一个存储，并把挂载命令写入fstab文件，如下：
...
192.168.1.235:/databak /db_backup  nfs     defaults        0 0

本以为这样挂载没问题，可昨天重启过机器后，发现晚上数据库备份失败了，备份日志如下：

;;; 
Export: Release 10.2.0.4.0 - 64bit Production on Wednesday, 05 March, 2014 6:30:01




Copyright (c) 2003, 2005, Oracle.  All rights reserved.
;;; 
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
ORA-39000: bad dump file specification
ORA-31641: unable to create dump file "/db_backup/jjsd_2014030505.dmp"
ORA-27054: NFS file system where the file is created or resides is not mounted with correct options
Additional information: 3


意思是文件mount不正确，警告日志里面也有类似输出

WARNING:NFS file system /db_backup mounted with incorrect options
WARNING:Expected NFS mount options: rsize>=32768,wsize>=32768,hard


看来，还是那个 defaults 的原因导致上面备份时的写权限问题，把它替换为具体的相关参数即可，比如警告日志里面的 options: rsize>=32768,wsize>=32768,hard