3.7.0 HP StorageWorks HP Scalable NAS File Serving Software provisioning guide for Oracle HP Scalable NAS (AG513-96013, October 2009)

Managing Virtual NFS Services using Direct NFS
Beginning with Oracle 11g, Oracle includes their own NFS client, Direct NFS, which
can be used to access data files over NFS. However, it is not used to access Oracle
Home, CRS voting or registry files, or other files via NFS. For that, Linux-based Oracle
servers use the NFS client provided by the operating system. This distinction is
important because only those objects supported by Direct NFS will have the added
workload balancing and high availability features brought by Direct NFS.
By default, Direct NFS is not active. To use the Direct NFS client, before starting the
database, you must both (1) deploy the Direct NFS ODM library and (2) configure
the Direct NFS mounts for a given datafile, otherwise you will not be using Direct
NFS to access that datafile.
In the case of Linux Oracle servers, when accessing datafiles over NFS, if you do
not activate and configure Direct NFS, you will fall back to the typical 10g
configuration by automatically using the Linux operating system NFS client instead.
However, in the case of Windows-based Oracle (which does not support Oracle
over NFS prior to 11g) there is no other option that is available to access datafiles
over NFS. If Direct NFS is not configured on Windows, there is no way for Oracle
to access data files using NFS. Of course you can mount them using other NFS
implementations and see the files, but the Oracle database will not see them. In
addition, as of version 11.1.0.7, CRS voting and registry files are not yet supported
over NFS, even by third-party NFS clients. See Chapter 5, page 47, for more
information about a Windows-based deployment.
The advantages of using Direct NFS are many:
• Oracle has optimized the NFS client for accessing datafiles.
• Oracle’s Direct NFS client can load balance the I/O workload across up to four
paths to the NFS server exporting a datafile. Beginning with 11.1.0.7, you can
load balance across outbound paths on the client.
• Direct NFS can survive path failures as long as there is at least one path remaining
to the NFS server. These multiple paths can even be on the same network; it is
not necessary to use IP bonding to create these multiple paths. However, if a
physical IP address is used to define these paths, should all paths fail to the
server, or should the VNFS server fail (unlikely if using HP Scalable NAS), the
instance will shutdown.
• The mount options you select for accessing datafiles do not matter when accessing
datafiles with Direct NFS.
Oracle provides many ways to specify the network topology. In the absence of
anything else, Oracle will use /etc/mtab to determine paths, but this is limited to
Oracle DBA: managing Oracle databases in a NAS environment38