Automatic Storage Management (ASM)

This chapter covers the Automatic Storage Management (ASM) feature introduced in Oracle Database 10g, for efficient management of disk drives with round-the-clock (24x7) availability. ASM simplifies disk-space management by creating disk groups, which are comprised of disks and the files that reside on them. Using ASM, the DBA needs to manage a smaller number of disk groups. All you have to do for disk management is to allocate disks to Oracle with your preferences for striping and mirroring using templates and let the database handle the storage-management issues.

ASM helps resolve the routine disk-management problems of large Oracle databases. It also manages disks across multiple nodes of a cluster in RAC as in standalone servers. ASM prevents hot spots and improves performance by load-balancing across available disk drives and prevents fragmentation of disks. ASM allows for incremental addition and removal of disks and reduces DBA or system administrator intervention in database file management.

Multiple Oracle Instances Using ASM on a Single Server

If you have more than one Oracle Database 10g instance on a single system using ASM for database file storage, you should set up different Oracle homes for the database instances and run the CSS daemon and the ASM instance from the same ORACLE_HOME directory. The oracle user for each database instance should be a member of the dba group for the ASM instance and the disks must have read/write permission to the ASM dba group. The ASM oracle user does not need to be in the dba group as users of other database instances.

Stop all Oracle ASM instances and any Oracle database instances that use ASM for database file storage under all ORACLE_HOMEs. As root, identify the ORACLE_HOME directory used to run the CSS daemon. It will be /etc/oracle/ocr.loc for AIX and Linux, /var/opt/oracle/ocr.loc for other UNIX operating systems, and \oracle\ocr.loc for Windows. The ocrconfig_loc parameter (located in ORACLE_HOME/cdata/localhost/local.ocr) specifies the location of the Oracle Cluster Registry (OCR) used by the CSS daemon. Change the ORACLE_HOME to the new_ORACLE_HOME directory of the Oracle Database 10g installation from which you want the CSS daemon to run. Reconfigure the CSS daemon to run from this Oracle home as follows:

 $ORACLE_HOME/bin/localconfig reset $new_ORACLE_HOME 

This will stop the Oracle CSS daemon, reconfigure it in the new Oracle home, and then restart it. When the system reboots, the CSS daemon starts automatically from the new Oracle home. When you configure the CSS daemon to run from new_ORACLE_HOME, the ASM instance can be started in this new Oracle home. The other database instances running should be able to access this ASM instance and the underlying disks with appropriate permissions.

ASM integrates the file system and volume manager functionalities for Oracle database files. It removes the need for manual I/O tuning and extends the concept of stripe-and-mirror-everything (SAME) for better performance.