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General Parallel File System - GPFS

Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.

With AIX 5.1 (5L), database files can also be placed on GPFS. In this case, create a GPFS capable of holding all required database files, control files, and log files. GPFS is only supported with HACMP/ES in a RAC configuration. When placing data files on GPFS, no CRM (Concurrent Resource Manager) needs to be installed.

GPFS is a clustered file system defined over multiple nodes. GPFS is a high-performance, scalable file system designed for cluster environments. It allows users shared access to files that may span multiple disk drives on multiple nodes. It offers many of the standard UNIX file system interfaces, allowing most applications to execute without modification or recompiling. UNIX file system utilities are also supported by GPFS. It allows both parallel and serial applications running on different nodes to share data spanning multiple disk drives attached to multiple nodes. See Figure 6.16.

Figure 6.16: AIX Cluster Environment

A GPFS cluster in an HACMP environment is formed by a group of RS/6000 and IBM pSeries machines taking part in an HACMP/ES cluster. In this environment, every node in the GPFS cluster must be connected to the disks through their physical attachment so that each disk is available to all nodes for concurrent access.

GPFS operates under the HACMP/ES cluster environment. HACMP/ES provides the logical volume manager (LVM) subsystem. GPFS administrative scripts to each node in the cluster vary - on the volume groups containing the GPFS data - at proper times for file system operations. This GPFS operation is done without locking the disks that make up the volume group using the varyonvg command with the -u flag.

Disks for a GPFS file system now support both SSA and fiber channel attachment. Once the file system is created, it can be automatically mounted whenever the GPFS daemon is started. The auto-mount feature assures that whenever the system and disks are up, the file system will be available.

The Concurrent Logical Volume Manager (CLVM) component of AIX is not required for a GPFS cluster in a HACMP environment. The GPFS kernel extension provides the interfaces to the operating system VNODE and virtual file system (VFS) interfaces for adding a file system. Structurally, applications make file system calls to the operating system, which presents them to the GPFS file system kernel extension. In this way, GPFS appears to applications as just another file system. The GPFS daemon performs all I/O and buffer management for GPFS. This includes read-ahead for sequential reads, and write-behind for all writes not specified as synchronous. All I/O is protected by token management, which ensures that the file system on multiple nodes honors the atomicity and provides data consistency for a file system. The daemon is a multi-threaded process with some threads dedicated to specific functions.

GPFS performs all file system functions, including metadata functions, on all members of the cluster both within a file and across different files in a file system. When an inoperative node is detected by group services, GPFS fences it out using environment-specific subsystems. This prevents any write operations that might interfere with recovery.

With this review of the variety of ways the cluster software is installed and configured concluded, it is time to switch gears and begin looking into Oracle RAC software installation in the next section.


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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