Oracle Direct NFS (dNFS) is an NFS client which resides within the database kernel and should be enabled on Exadata for all direct database and RMAN workloads between Exadata and the Oracle ZFS Storage Appliance. With this feature enabled, you will have increased bandwidth and reduced CPU overhead. Even though there are no additional steps are required to enable dNFS although it is recommended to increase the number of NFS server threads from default to 1000.
As per Oracle documentation, using Oracle Direct NFS with Exadata can provide following benefits.
- Significantly reduces system CPU utilization by bypassing the operating system (OS) and caching data just once in user space with no second copy in kernel space
- Boosts parallel I/O performance by opening an individual TCP connection for each database process
- Distributes throughput across multiple network interfaces by alternating buffers to multiple IP addresses in a round-robin fashion
- Provides high availability (HA) by automatically redirecting failed I/O to an alternate address
In Oracle Database 12c, dNFS is already enabled by default. In 11g, Oracle Direct NFS may be enabled on a single database node with the following command:
$ make -f $ORACLE_HOME/rdbms/lib/ins_rdbms.mk dnfs_on
Exadata dcli may be used to enable dNFS on all of the database nodes simultaneously:
$ dcli -l oracle -g /home/oracle/dbs_group make -f $ORACLE_HOME/rdbms/lib/ins_rdbms.mk dnfs_on
Note: – The database instance should be restarted after enabling Oracle Direct NFS.
You can confirm that dNFS are enabled by checking the database alert log:
“Oracle instance running with ODM: Oracle Direct NFS ODM Library Version 3.0”
You can also use following SQL Query to confirm dNFS activity:
SQL> select * from v$dnfs_servers;