RAC on ASM and a Cluster File System
Oracle RAC systems are comprised of multiple database instances sharing the same database files. The shared database files include the data files, control files and online redo logs. Each instance writes to and reads from the same database files simultaneously. For the shared files to be available to processes on multiple machines, the disks containing the files must be shared. With Oracle 10g, a clustered file system is available for free on Linux and Windows systems named Oracle Cluster File System (OCFS). Deploying OCFS to a shared disk device like a storage area network allows database files to be shared between multiple instances. Another disk management system new to Oracle 10g is named Automatic Storage Management (ASM). Oracle can allocate a disk group on a storage device unit and place Oracle database files within this disk group. From the operating system, the Oracle disk group cannot be managed by typical operating system file commands. Management of the files must be done via Oracle’s database instance. A RAC database can have files on both OCFS and ASM file systems simply by specifying the file location when creating the files.
