An ASM instance is NOT backed up. ASM instance itself does not contain any files but manages the metadata of the ASM disks. Just as you cannot backup or restore this sort of information for a filesystem, you cannot do so for ASM. ASM metadata is triple mirrored, which should protect the metadata from typical failures. If sufficient failures occur to cause the loss of metadata, the diskgroup must be recreated.

Data on the ASM disks is backed up using RMAN. In case of failure, once the diskgroups are created the data (such as database files) can be restored using RMAN.

In other words, The ASM instance is just another volume manager like VxFS. You would not backup the VxFS information just reinstall and rebuild if a failure occurs. This is the same situation with ASM. Also, the disk partitions used by ASM comprise multiple databases. When any action performed will overwrite the database information of all databases making use of this ASM instance.

If a DBA would like to retain information on the ASM system, they can keep record of the settings for the init.ora parameters asm_diskgroups and asm_diskstring. A register document can be created, which essentially would be a spool of the information in V$ASM_..... views.


NOTE: In Oracle11g, ASMCMD is extended to include ASM disk group metadata backup and restore functionality.


출처 : metalink