Oracle Automatic Storage Management with Oracle RAC
Oracle Automatic Storage Management (Oracle ASM) automatically maximizes I/O performance by managing the storage configuration across the disks that Oracle ASM manages.
Oracle ASM does this by evenly distributing the database files across all of the available storage assigned to the disk groups within Oracle ASM. Oracle ASM allocates your total disk space requirements into uniformly sized units across all disks in a disk group. Oracle ASM can also automatically mirror files to prevent data loss. Because of these features, Oracle ASM also significantly reduces your administrative overhead.
Oracle ASM instances are created on each node where you install Oracle Grid Infrastructure. Each Oracle ASM instance has either an SPFILE or PFILE type parameter file. Oracle recommends that you back up the parameter files and the TNS entries for nondefault Oracle Net listeners.
To use Oracle ASM with Oracle Real Application Clusters (Oracle RAC), select Oracle ASM as your storage option when you create your database with the Oracle DBCA. As in noncluster Oracle AI Database, using Oracle ASM with Oracle RAC does not require I/O tuning.
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Storage Management in Oracle RAC
You can create Oracle ASM disk groups and configure mirroring for Oracle ASM disk groups using the Oracle ASM configuration assistant (ASMCA).
Alternatively, you can use Oracle Enterprise Manager to administer Oracle ASM disk groups after you have discovered the respective servers with Oracle Enterprise Manager.
The Oracle tools that you use to manage Oracle ASM, including ASMCA, Oracle Enterprise Manager, and the silent mode install and upgrade commands, include options to manage Oracle ASM instances and disk groups.
You can use the Configuration Verification Utility (CVU) to verify the integrity of Oracle ASM across the cluster. Typically, this check ensures that the Oracle ASM instances on all nodes run from the same Oracle home and, if asmlib exists, that it is a valid version and has valid ownership. Run the following command to perform this check:
cluvfy comp asm [-n node_list] [-verbose]Replace node_list with a comma-delimited list of node names on which the check is to be performed. Specify all to check all nodes in the cluster.
Use the cluvfy comp ssa command to locate shared storage.
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Modifying Disk Group Configurations for Oracle ASM
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 AI 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 AI Database, 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. 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.
Note:
When you start ASMCA, if there is not an Oracle ASM instance, then the utility prompts you to create one.
Oracle ASM Disk Group Management
To use Oracle ASM, you must first create disk groups with ASMCA before creating a database with Oracle DBCA.
You can also use the disk group management commands to create and manage an Oracle ASM instance and its associated disk groups independently of creating a database. You can use Oracle Enterprise Manager or ASMCA to add disks to a disk group, to mount a disk group or to mount all of the disk groups, or to create Oracle ASM instances. Additionally, you can use Oracle Enterprise Manager to dismount and drop disk groups or to delete Oracle ASM instances.
Oracle ASM instances are created when you install Oracle Grid Infrastructure. To create an Oracle ASM disk group, run ASMCA from the Grid_home/bin directory. You can also use the Oracle ASM Disk Groups page in ASMCA for Oracle ASM management. That is, you can configure Oracle ASM storage separately from database creation. For example, from the ASM Disk Groups page, you can create disk groups, add disks to existing disk groups, or mount disk groups that are not currently mounted.
When you start ASMCA, if the Oracle ASM instance has not been created, then ASMCA prompts you to create the instance. ASMCA prompts you for the sysasm password and the ASMSNMP password.
Configuring Preferred Mirror Read Disks in Extended Distance Clusters
You can configure preferred read disks to improve performance.
When you configure Oracle Automatic Storage Management (Oracle ASM) failure groups, it may be more efficient for a node to read from an extent that is closest to the node, even if that extent is a secondary extent. You can configure Oracle ASM to read from a secondary extent if that extent is closer to the node instead of Oracle ASM reading from the primary copy which might be farther from the node. Using preferred read failure groups is most beneficial in an extended distance cluster.
To configure this feature, set the ASM_PREFERRED_READ_FAILURE_GROUPS initialization parameter to specify a list of failure group names as preferred read disks. Oracle recommends that you configure at least one mirrored extent copy from a disk that is local to a node in an extended cluster. However, a failure group that is preferred for one instance might be remote to another instance in the same Oracle Real Application Clusters (Oracle RAC) database. The parameter setting for preferred read failure groups is instance specific.
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Converting Nonclustered Oracle ASM to Clustered Oracle ASM
When installing Oracle Grid Infrastructure, any nonclustered Oracle Automatic Storage Management (Oracle ASM) instances are automatically converted to clustered Oracle ASM.
Administering Oracle ASM Instances with SRVCTL in Oracle RAC
You can use the Server Control Utility (SRVCTL) to add or remove an Oracle ASM instance.
To issue SRVCTL commands to manage Oracle ASM, log in as the operating system user who owns the Oracle Grid Infrastructure home and issue the SRVCTL commands from the bin directory of the Oracle Grid Infrastructure home.
Use the following syntax to add an Oracle ASM instance:
srvctl add asmUse the following syntax to remove an Oracle ASM instance:
srvctl remove asm [-force]You can also use SRVCTL to start, stop, and obtain the status of an Oracle ASM instance as in the following examples.
Use the following syntax to start an Oracle ASM instance:
srvctl start asm [-node node_name] [-startoption start_options]Use the following syntax to stop an Oracle ASM instance:
srvctl stop asm [-node node_name] [-stopoption stop_options]Use the following syntax to show the configuration of an Oracle ASM instance:
srvctl config asm -node node_nameUse the following syntax to display the state of an Oracle ASM instance:
srvctl status asm [-node node_name]Related Topics