When you create a disk group for a cluster or add new disks to an existing clustered disk group, prepare the underlying physical storage on shared disks and give the Oracle user permission to read and write to the disk. The shared disk requirement is the only substantial difference between using Oracle ASM with an Oracle RAC database compared to using it with a noncluster Oracle database. Oracle ASM automatically redistributes the data files after you add or delete a disk or disk group.
In a cluster, each Oracle ASM instance manages its node's metadata updates to the disk groups. In addition, each Oracle ASM instance coordinates disk group metadata with other nodes in the cluster. As with noncluster Oracle databases, you can use Oracle Enterprise Manager, ASMCA, SQL*Plus, and the Server Control Utility (SRVCTL) to administer disk groups for Oracle ASM that are used by Oracle RAC. The Oracle Automatic Storage Management Administrator's Guide explains how to use SQL*Plus to administer Oracle ASM instances. Subsequent sections describe how to use the other tools.
When you start ASMCA, if there is not an Oracle ASM instance, then the utility prompts you to create one.