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Before the dNFS driver is configured or used on an NFS share, the NFS share must first be mounted using the native NFS driver (kNFS). Specific mounting options are required when mounting an NFS share for Oracle usage. If the NFS export will be used for Oracle services that are to be automatically restarted when the server restarts, add the NFS export and mount options to /etc/fstab. If the NFS share and mount options are not specified in /etc/fstab, Oracle will experience issues if the Oracle servers are set to auto start during a Linux boot. In an Oracle RAC cluster, ensure that all nodes in the cluster use the same mount options and /etc/fstab entry for each identical NFS share mount point.
After the NFS share is mounted using kNFS, dNFS mounts and unmounts the NFS share logically as needed. Because dNFS uses a logical mount, after Oracle unmounts the NFS share, the NFS share is still physically mounted to the server and can be accessed through kNFS.
If NFS is used for database files, the NFS buffer size for reads (rsize) and writes (wsize) must be set to at least 16,384. Oracle recommends a value of 32,768. For the NFS client, these values are set in /etc/fstab or when explicitly mounting an NFS share. For performance reasons, Dell Technologies recommends evaluating whether rsize and wsize should be changed from the Oracle default.
Unity NAS servers support a range of values for rsize, and wsize in 8 KiB increments starting from 8192 to 1048576. The default value of Unity’s rsize and wsize is in Unity parameter nfs.v3xfersize. Its value is set depending on the amount of memory in the system. For the Unity system used for this paper, a default of 262144 was set for both rsize and wsize. dNFS clients issue writes with Oracle v$dnfs_servers.wtmax granularity to the Unity NAS server. Dell Unity NAS facility parameter nfs.v3xfersize.current_value specifies the size of I/Os to and from the Unity NAS server. nfs.v3xfersize.current_value must be a multiple of v$dnfs_servers.wtmax.
Note: Changing the rsize or wsize on the Unity NAS server requires a restart of the SP. For more information, see the sections Dell Unity Service Scripts and Unity’s nfs.v3xfersize parameter.
For additional mount options and information about using NFS shares intended for Oracle, see the Oracle MOS notes listed in Oracle Support MOS notes.