NFS and Oracle

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On nfsserver, create or edit /etc/exports with the following line (`man exports' for more options):
/ext *(rw,sync)
Then:
exportfs -a
service nfs start

On nfsclient that wishes to NFS-mount this share:
mkdir /ext
mount -t nfs nfsserver:/ext /ext

Once done, umount. If device busy, fuser /ext, fuser /ext/*, fuser /ext/*/*, etc. Or umount -l.
On nfsserver, showmount; service nfs stop

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Data Pump Import issue:

Ref: ORA-39000 ORA-31640 ORA-27054 Errors On Invoking DataPump Import (IMPDP) (Doc ID 739570.1)
--- begin quote ---
If you get errors running impdp:

ORA-39001: invalid argument value
ORA-39000: bad dump file specification
ORA-31640: unable to open dump file "<Dump file path>" for read
ORA-27054: NFS file system where the file is created or resides is not mounted with correct options
Additional information: 3 

You need these mount options:
rsize=32768,wsize=32768,hard,actimeo=0
--- end quote ---
If that doesn't work, i.e. after
mount -t nfs -o rsize=32768,wsize=32768,hard,actimeo=0 nfsserver:/ext /ext
you still get the errors, do:
alter system set events '10298 trace name context forever, level 32';
That event disables several (5?) checks of Oracle files, probably including corruption check. Once 
done, clear it:
alter system set events '10298 trace name context off';
alter system reset event scope = spfile sid = '*' <-- RAC only

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Automount must ensure the correct mount option as well. Find the options in relevant files 
(/etc/auto.<something>, check /etc/auto.master) and change, e.g. soft to hard, etc. Then `service 
autofs restart'.

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RMAN:

RMAN operation across NFS needs event 10298 too. See above for syntax.

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dNFS:

On nfsserver, /etc/exports:
/u01/yongtemp *(rw,insecure,no_root_squash)
insecure according to ASM Diskgroup on NFS: ORA-15080 ORA-17500: ODM err: (Doc ID 2203220.1)
On nfsclient:
mount -t nfs -o hard,intr,rsize=32768,wsize=32768,noatime,vers=3 nfsserver:/u01/yongtemp /yongtemp
vers=3 because Direct NFS: FAQ (Doc ID 954425.1) "dNFS on Oracle 11g will only work with NFSv3 volumes.Direct NFS Client (dNFS) supports NFS V4 in Oracle Database 12c."

After bouncing instance:

SQL> select * from v$dnfs_servers;

        ID SVRNAME      DIRNAME          MNTPORT    NFSPORT      WTMAX      RTMAX
---------- ------------ ------------- ---------- ---------- ---------- ----------
         1 nfsserver    /u01/yongtemp      43215       2049    1048576    1048576

After expdp to the dNFS mount point, these 5 columns have non-zero values:

SQL> select pnum, nfs_setattr, nfs_lookup, nfs_write, nfs_writebytes from gv$dnfs_stats where NFS_NULL+NFS_GETATTR+NFS_SETATTR+NFS_LOOKUP+NFS_ACCESS+NFS_READLINK+NFS_READ+NFS_WRITE+NFS_CREATE+NFS_MKDIR+NFS_SYMLINK+NFS_MKNOD+NFS_REMOVE+NFS_RMDIR+NFS_RENAME+NFS_LINK+NFS_READDIR+NFS_READDIRPLUS+NFS_FSSTAT+NFS_FSINFO+NFS_PATHCONF+NFS_COMMIT+NFS_MOUNT+NFS_READBYTES+NFS_WRITEBYTES>0;

      PNUM NFS_SETATTR NFS_LOOKUP  NFS_WRITE NFS_WRITEBYTES
---------- ----------- ---------- ---------- --------------
        85         139          2      34686     9080958976

Test of performance: no advantage over regular NFS