Improved NFS Performance/Management in 11g

Oracle 11g has introduced a new method for directly accessing NFS V3 servers by using an internal Direct NFS Client as part of the Oracle Database kernel.  This improves performance and manageability by allowing Oracle-specific optimizations to be utilized.  Additionally, it removes the need to manually configure and tune most of the NFS client parameters.

The use of network attached storage (NAS) systems has become increasingly common in enterprise database environments.  This is due to the growing need to consolidate data to a single point of access.  NAS technology offers an ideal solution to this need by allowing access to network drives as if they were directly attached to the client.  This allows the users, applications, or the database itself to access files stored on the network as if they were stored on local drives. 

Files used by the database can be stored on the NFS drive, including data files.  However, due to the performance limitations of NFS storage prior to Oracle 11g, many production databases opted to use network storage for files and processes. With these, the performance limitation was acceptable.  Using NFS drives allows for scalability of disk space without requiring an upgrade of the existing architecture.  Now the system administrator can attach a network drive and access the drive as if it was attached locally.  Once the network drive is available, data files can be moved or created in the newly available drives. 

NFS drives provide a common access point between multiple systems that are unable to directly connect to each other but can independently connect to the network file system.  This is a common situation that can arise from a multitude of reasons.  For example, security protocol on a server that supports an ERP database generally restricts other systems from direct access.  However, the ERP database might have several dependencies on external systems, such as systems that support electronic data interchange (EDI).  By utilizing a network drive, the data transmission can flow from the external systems into the ERP system without the two systems ever being directly connected.  There are many other uses for NFS storage and as enterprise systems grow in size, the importance of this technology in a system's architecture will become increasingly important.

Prior to the 11g release of Oracle, the benefits of NFS and the database have been subject to certain drawbacks such as performance degradation and complex configuration requirements of the NFS client. These drawbacks have been minimized in Oracle 11g by the integration of a direct NFS client in the Oracle kernel.  This client allows Oracle to optimize the I/O path between Oracle and the NFS server directly.  Utilizing Oracle's direct NFS client is also automated and simplified in configuration to achieve optimal performance. 

Benefits of Direct NFS

The direct NFS client has two fundamental optimizations that increase performance.  First, the direct NFS client is capable of performing concurrent direct I/O. This removes the need to utilize the operating system's cache and bypassing limitations which are imposed by the operating system configuration.  Using the operating system to configure the NFS client, and data written from the database to the NFS, requires that the data be read from Oracle's memory to the operating system cache.  This is done before it is copied from the system cache to the NFS. By using the direct NFS client, the Oracle data no longer needs to be cached in the operating system.  The process reduces the overall memory consumption and kernel CPU when writing to the network drive. 

In addition to eliminating the dependency on the operating system cache, the second fundamental optimization is that the direct NFS client now supports asynchronous I/O on NFS file systems.  Asynchronous I/O (AIO), also known as non-blocking I/O, allows I/O processing to continue independently from other I/O that has not yet completed.  This setting makes a tremendous difference for read/write performance, whether using an NFS or a local drive.  Many DBAs have experience enabling AIO on their local file systems and recall the performance improvement when switching from synchronous I/O to asynchronous I/O.  As of Oracle 11.1, the direct NFS client supports up to four parallel network paths.  The direct NFS client automatically performs load balancing across all specified paths.  

Another advantage of the direct NFS client is that Oracle manages the configuration across different platforms.  This greatly simplifies the task of administering NFS storage by allowing Oracle to internally manage the NFS configurations for all platforms.  This eliminates the need to manage different configurations on each platform, or use storage-specific drivers.  This feature also uses simple Ethernet for storage connectivity, eliminating the need for additional architecture components such as redundant host bus adaptors, Fiber channel switches, or bonded network interfaces. 

The direct NFS client supports both single instance databases as well as real application cluster (RAC) environments.  The client recognizes when an instance is part of a RAC environment and automatically optimizes the NFS configuration accordingly.