What Is ASM?
ASM is a combination of a logical volume manager and a file system embedded within the database. Using ASM, you define groups of disks that are analogous to the volumes you would otherwise create by using an LVM.
In an Oracle Clusterware environment, the individual ASM instances, one per node, cooperate to
offer shared disk group access across the cluster.
The ASM instances are under the control of Oracle Clusterware. Oracle Clusterware manages the start, stop and health check functions for the ASM instances just as it does for RAC database
instances. Oracle Clusterware also ensures that the RAC database instances and the ASM instance start and shutdown in the proper order (that is, the ASM instance starts up before the database instances and shuts down after the database instances).
The keywords NORMAL REDUNDANCY result in two-way mirroring of all files on the disk group. You can specify EXTERNAL REDUNDANCY if your disks each map to a RAID array managed externally or if you do not care to mirror the files at all. You can be
extra cautious and specify HIGH REDUNDANCY to get three-way mirroring.
Placing new objects on a disk group is simple. You can use disk group names in place of filenames when you create database files, redo log members, and so on. Even though you're now using ASM storage, you perform these operations while connected to your database instance. For example,
CREATE TABLESPACE geo_names
DATAFILE '+MYDATA' SIZE 100M;
The plus sign (+) in front of the name MYDATA indicates that the name is a disk group name, not an operating system filename.
ASM 11gR2 new features:
1. Installation : Significant Changes
• New (complex) network requirements
• New GRID user + environment
• 2 Oracle Homes (instead of 3)
– ASM and CRS together in GRID home
– Must be different ORACLE_BASE
– Unset env vars before installing
• OCR/Vote not supported on raw
– Use ASM or CFS instead
• Cluster Time Synchronization Service
• Software only Grid install possible
Administration: Significant Changes
• User specific actions (grid, oracle, root)
• Startup & shutdown
• Cluster status crs_stat deprecated
• Listener configuration
• Client configuration (tnsnames)
• OCR/Vote Disk backup
• ACFS management