Oracle Direct NFS: How to Start

Jun 30, 2012 / By Yury Velikanov

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First of all, if you are using NFS to store Oracle database data files, I strongly advise you to enable Oracle Direct NFS (DNFS) to access these files. I will leave the long explanation on why you should do it out of this blog post. However, I’ll mention that the main reason is performance. (Google it or wait for my following blog posts for more information.) DNFS removes a serialization point over the traditional “kernelized” NFS. However, if you are not using NFS, DNFS is probably not of interest to you, and you should stop reading here. But, if you want to set it up, let’s go! :)

The only legitimate reason I can see for not using DNFS is a bug that doesn’t allow you to use it. If this is the case, I would advise you to resolve the problem (probably by applying a patch from Oracle Support) and enable DNFS.

How to set up

Reference: Step by Step – Configure Direct NFS Client (DNFS) on Linux (11g) [ID 762374.1]
One of DNFS’s greatest features is an easy way to enable/disable it and a relatively easy way to check if it’s enabled or not. It is worth mentioning that DNFS is available from Oracle 11G only. If your system is configured using NFS (see Oracle Support notes on how to configure it), use the following two commands to enable/disable DNFS.

  • Enable
ln -s $ORACLE_HOME/lib/ $ORACLE_HOME/lib/
  • Disable
ln -s $ORACLE_HOME/lib/ $ORACLE_HOME/lib/

Of course, you should stop all DBs that use the ORACLE_HOME, make a backup of the initial symbol link, etc. I’ll leave the precaution measures to you. The simple fact is that the two commands above are the only commands  you should know to enable/disable Oracle Direct NFS.

You would ask: How does Oracle know what NFS server to connect to, what IP to be used, etc? In the simplest configuration, Oracle retrieves all the information it needs from the /etc/mtab Linux configuration file. This file is populated by Linux each time you mount an NFS volume. The static volumes’ mount configuration is stored in an /etc/fstab file.

How to check

This is where the story gets a bit tricky. The Oracle Support note mentioned above [ID 762374.1] states the following:

alert log shows Direct NFS client is enabled by checking the below message
Oracle instance running with ODM: Oracle Direct NFS ODM Library Version 2.0

However, I came across several cases where the message was in an alert.log file, but DNFS still wasn’t enabled.
I found that the easiest and most reliable way to verify if DNFS is enabled and working as expected is to check Oracle Instances process’ opened files list. Find a process that has opened at least one data file and run lsof Linux command against the process. I usually check the DBWR foreground process as it has some data files opened right from the instance start up time.

The following is an example of how an output should look like if the DNFS is in use:

-bash-3.2$ ps -ef | grep dbw
oracle   23126     1  0 06:53 ?        00:00:00 ora_dbw0_MYINST1
oracle   23128     1  0 06:53 ?        00:00:00 ora_dbw1_MYINST1
oracle   23246 22377  0 07:04 pts/0    00:00:00 grep dbw
-bash-3.2$ /usr/sbin/lsof -p 23126
oracle  23126 oracle  cwd    DIR  104,3      4096   14811513 /u02/app/oracle/product/
oracle  23126 oracle  rtd    DIR  104,3      4096          2 /
oracle  23126 oracle  txt    REG  104,3 210824714   15892486 /u02/app/oracle/product/
oracle  23126 oracle   32u  IPv4 322388                  TCP mydbhost:64553->mynfshost:nfs (ESTABLISHED)
oracle  23126 oracle   33u  IPv4 322389                  TCP mydbhost:21549->mynfshost:nfs (ESTABLISHED)

Pay attention to the last two rows I highlighted. You should see just TCP/IP sockets opened by the process towards NFS server. There should not be any data files listed. If you see any of the data files (located on NFS) in the output, then the instance doesn’t use DNFS. BTW: I would appreciate if you provided an output with data files listed in the comments section below this blog post as I would like readers to see an example. Unfortunately, I don’t have a good (bad) example handy as all instances I have access to use DNFS today :).

At this point, I would like to end my very first DNFS-related blog post. I have a lot more to say about DNFS, but I’ll leave it for future blog posts. The following is just comments and questions I have about DNFS:

  • NFS server must be configured to accept NFS clients’ requests coming from a non-standard port range.
  • How to load balance DNFS traffic if you have several NICs (oranfstab file)?
  • Use init.ora parameters (events 19392, 19394, 19396) to troubleshoot DNFS configuration.
  • Don’t use the same NFS volumes names on different NFS servers (DNFS can’t work it out).
  • Performance difference between kNFS & DNFS (testing results). Is there any real benefits using DNFS over kNFS?
  • Good references list for DNFS information (MOS notes, Blog posts, etc.)
  • Some other details you want here :) …

Let’s hope that, with all your support and a bit of free time, I will blog about the topics mentioned :)

Stay tuned folks,

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13 Responses to “Oracle Direct NFS: How to Start”

  • Caden says:

    Finding this post svoles a problem for me. Thanks!

  • NFS Wonder says:

    From reading this post Direct NFS seems to be an alternative to kernel based NFS. What I wonder:

    Direct NFS reads NFS shares to mount from /etc/mtab. That means that I still need to mount these shares using kernel based NFS, else the shares wouldn’t appear there, right? So I need to setup kernel based shares anyway.

  • Rich Bernat says:

    I am switching over to Oracle dNFS for my Linux RHEL6 using NetApp Storage. So far so good but I have run into a problem where the orapw file is not read/processed when the Oracle Binaries are also on a remote source. Oracle nfs ODM seems to not read the orapw file in the dbs directory.

    The datafiles and the binaries are on separate mounts and from separate servers.

    I’ve got 4 NIC’s for the storage connections confirured and they are all working appropriately.

    If I relocate the pwfile into a put a symbolic link from teh dbs firectory to it.. the pwfile is recognized. And it worked fine without the Oracle dNFS enabled.

    The alert log shows the following:
    Oracle image stored on remote server servernas1

    Oracle instance running with ODM: Oracle Direct NFS ODM Library Version 3.0


    Completed: ALTER DATABASE open

    Errors in file /oracle/BDM/saptrace/diag/rdbms/bdm/BDM/trace/BDM_ora_10246.trc:
    ORA-17503: ksfdopn:3 Failed to open file /oracle/v11203a/dbs/orapwBDM
    ORA-17500: ODM err:No such file or directory

    This error is raised when performing a simple ‘select * from v$pwfile_users;’ or a grand sysdba to …

    Any thoughts as to what may be causing that? Is there any option to restrict Oracle dNFS from processing the binaries and the dbs directory ?


    • Hey Rich,

      Just a quick educated guess from my side quickly scanning morning emails.

      Can you check if NFS volumes from different Fillers have the same names: e.g. nfsserver01:/oravol1 and nfsserver02:/oravol1

      If this is the case then there is a known DNFS issue. I have faced it myself. Just rename volume to be unique across all NFS mounts on the DB server.


  • Barry Ghotra says:

    oracle 25696 oracle 16u REG 0,20 1544 51957 /u01/app/oracle/product/11.2.0/dbhome_2/dbs/hc_OEMREP.dat (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 17uR REG 0,20 24 51955 /u01/app/oracle/product/11.2.0/dbhome_2/dbs/lkOEMREP (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 18r REG 0,20 1101312 59735 /u01/app/oracle/product/11.2.0/dbhome_2/rdbms/mesg/oraus.msb (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 256u REG 0,20 10928128 781 /u01/oradata/OEMREP/control01.ctl (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 257u REG 0,20 10928128 782 /u01/FRA/OEMREP/control02.ctl (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 258uW REG 0,20 734011392 789 /u01/oradata/OEMREP/system01.dbf (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 259uW REG 0,20 629153792 790 /u01/oradata/OEMREP/sysaux01.dbf (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 260uW REG 0,20 613425152 791 /u01/oradata/OEMREP/undotbs01.dbf (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 261uW REG 0,20 5251072 793 /u01/oradata/OEMREP/users01.dbf (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 262uW REG 0,20 104865792 143808 /u01/oradata/OEMREP/mgmt_depot.dbf (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 263uW REG 0,20 2621448192 143809 /u01/oradata/OEMREP/mgmt.dbf (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 264uW REG 0,20 209723392 143810 /u01/oradata/OEMREP/mgmt_ad4j.dbf (ca-filer2:/vol/oraemsvrmnt/)
    oracle 25696 oracle 265uW REG 0,20 46145536 792 /u01/oradata/OEMREP/temp01.dbf (ca-filer2:/vol/oraemsvrmnt/)

  • hassan says:

    how should the mounts be defined —

    I have several linux oracle servers. We are moving from Netapp to EMC. Only one of linux oracle servers is going to mount to our new EMC vnx5300.

    I am getting the error


    ORACLE instance started.

    Total System Global Area 2488709120 bytes

    Fixed Size 2162200 bytes

    Variable Size 469762536 bytes

    Database Buffers 2013265920 bytes

    Redo Buffers 3518464 bytes



    ERROR at line 1:

    ORA-01503: CREATE CONTROLFILE failed
    ORA-00200: control file could not be created
    ORA-00202: control file: ‘/oracle11/oradata/rlispub/control01.ctl’
    ORA-17502: ksfdcre:/oracle11/oradata/rlispub/control01.ctl Failed to create file

  • Jesse Sunkara says:

    An easier way to verify and view the DNFS stats would be to query the dnfs v$ views:
    SQL> select * from v$dnfs_servers;
    SQL> select * from v$dnfs_files;
    SQL> select * from v$dnfs_files;
    SQL> select * from v$dnfs_channels;

    • My point and warning to outside world V$ views sometimes aren’t reliable source of information. I was there myself.
      On the side note for some geeky folks “lsof” option may be much easier than SQL :)

      PS Thanks for the comment Jesse

  • ???????, ???! ???? ?????? ?????? ? 1-? ??????? ?? ???? DirectNFS ? Google, ????? ??? ??? ????????????. ???? ????????? ????? ?? ?????? ?????? ?????? ? MOS.
    ??? ????? ?????? ? ???, ??? ??? ?????????? (??? ????? ??? ?, ??? ????, ?? ??????? ????? ???????????) ??? ??? ??????? ??????.
    ? MOS ?????? ?? ??????? ????? ????? ?? ???????????, ??? ??????? ?????????, ? ????? ????? ????? ? CloneDB. ?????? ?????? ? ??????????? – ?????? ? ??? ???? – ??? ????? ????????? ??? ????????? NetApp.

  • ops. :(
    1) Pythian web site does not support Unicode despite sourse shows: meta charset=”UTF-8″ Yura, please help your web-admins to setup NLS settings.
    2) Build using Ajax approach

    about Direct NFS:
    1. Saved me some minuted looking for right MOS article when ai needed it. Thank You! It is in top 10 in Google search for the subject.
    2. Another benefit – article reminds (to some like me, that was learning DNFS feature, but had forgotten because not using)
    3. MOS article have links to others, one of them have presentation that explain internals as well as new DNFS based feature CloneDB.
    If will investigate the DNFS again – take a look. This may be very attractive for big DB like in banks and for NetApp lovers.
    MOS notes recommended:
    * Step by Step – Configure Direct NFS Client (DNFS) on Linux (11g) [ID 762374.1] (yours)
    * DNFS: Example About How To Setup DNFS (Direct NFS) On Oracle Release 11.2 [ID 1452614.1]
    * Recommended Patches for Direct NFS Client [ID 1495104.1]

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