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Oracle dNFS is an optimized NFS client from Oracle for database I/O and resides in the ODM library as a part of the Oracle database kernel. dNFS improves the stability and reliability of NFS storage devices over TCP/IP, more so than the native Linux NFS driver (kNFS). dNFS also improves performance to NFS storage devices by bypassing the kNFS I/O stack. When mounting the database datafiles, Oracle will first load dNFS functionality if the Direct NFS client ODM library is enabled. If dNFS cannot access an NFS storage device, dNFS silently reverts to using the kNFS client driver. However, to ensure this reversion occurs, the kNFS client mount options rsize and wsize must be used.
It is recommended to use dNFS if NFS storage devices are used by an oracle database so that the performance optimizations and multipathing built into Oracle can be exploited.
To use Oracle dNFS with Unity storage, use NFS protocol NFSv3, and enable Unity’s nfs.transChecksum NAS server parameter (set to 1). This parameter ensures that each transaction carries a unique ID and avoids the possibility of conflicting IDs that result from the reuse of relinquished ports. For more information about nfs.transChcksum and how to configure it, see the section Dell Unity Service Scripts and Dell Unity document: Dell Unity Family Service Commands Technical Notes.