6. Launch SQL*Plus. Connect to the ASM instance as SYSASM, and query views that describe your ASM files and disk groups.
select * from v$asm_file;
select * from v$asm_diskgroup;
Note the correspondence with the results of Steps 2 and 3.
Two-Minute Drill
Describe Automatic Storage Management (ASM)
• ASM is a logical volume manager, providing striping and (optionally) mirroring of Oracle database files.• The files that can be stored on ASM devices include datafiles; tempfiles; the controlfile; online and archive redo log files; the spfile; RMAN backup sets; and image copies.• You cannot use ASM devices for the Oracle binaries or diagnostic and trace files.• ASM will always stripe files across all disks in a disk group, but mirroring is optional.• The default mirroring is NORMAL REDUNDANCY (meaning two copies of each allocation unit), but this can be adjusted to EXTERNAL REDUNDANCY (one copy only), or to HIGH REDUNDANCY (three copies) if the group has at least three disks.• The cluster services are required (even in a non-RAC environment) to set up
PART IIIthe connections between RDBMS instances and an ASM instance.• No data ever passes through an ASM instance. ASM is responsible only for managing the storage structures; the RDBMS instance(s) perform the I/O operations.
Set Up Initialization Parameter Files for ASM
and Database Instances
• The parameter INSTANCE_TYPE must be set to either RDBMS (the default) or ASM to control whether the instance is a database instance or an ASM instance.• An ASM instance should have the ASM_DISKSTRING and ASM_DISKGROUP parameters set to identify the disks that the ASM instance may use and the disk groups it should mount. These parameters are illegal in an RDBMS instance.• Very few parameters are legal in an ASM instance. Usually INSTANCE_TYPE, INSTANCE_NAME, and the ASM prefixed parameters are all that are needed.
Start Up and Shut Down ASM Instances
• You can connect to an ASM instance only with operating system or password file authentication, as SYSDBA or SYSASM (though SYSDBA is only supported for backward compatibility).• An ASM instance can be started only in NOMOUNT mode. It will never mount a controlfile nor open any datafiles—though it will mount disk groups to make them available to RDBMS instances.• An ASM instance cannot be shut down (other than with an ABORT) if an RDBMS instance has opened files in disk groups it is managing.
Administer ASM Disk Groups
• Disk groups are made up of one or more discovered disks.• Files created in ASM disk groups consist of 1MB allocation units, distributed across all the disks in the group.• ASM files can be backed up only with RMAN; operating system utilities cannot see the files in a disk group.• Disks can be added to and removed from a disk group dynamically. The allocation units of the files will be restriped by an automatic rebalancing operation to take advantage of any new disks, or to reestablished mirrors if a disk is removed.• Disk groups can be mounted manually with the ALTER DISKGROUP MOUNT command, or automatically by nominating them in the ASM_DISKGROUPS parameter.
Self Test
