Oracle Database 10g Automatic Storage Management Concepts and Administration

ASM Instance Functionalities

The main goal of an ASM instance is to manage disk groups and protect their data. ASM instances also communicate file layout to database instances. In this way, database instances can directly access files stored in disk groups.
There are several new disk group administrative commands. They all require the SYSDBA privilege and must be issued from an ASM instance.You can add new disk groups. You can also modify existing disk groups to add new disks, remove existing ones, and many other operations. You can remove existing disk groups.
Finally, you can prevent database instances from connecting to an ASM instance. When the command ALTER SYSTEM ENABLE RESTRICTED SESSION is issued to an ASM instance, database instances cannot connect to that ASM instance. Conversely, ALTER SYSTEM DISABLE RESTRICTED SESSION enables connections from database instances. This command permits an ASM instance to start up and mount disk groups for purposes of maintenance without allowing database instances to access the disk groups.

ASM Instance Initialization Parameters

INSTANCE_TYPE should be set to ASM for ASM instances.
DB_UNIQUE_NAME specifies the service provider name for which this ASM instance manages disk groups.The default value of +ASM should be valid for you. It needs to be modified only if you try to run multiple ASM instances on the same node.
ASM_POWER_LIMIT controls the speed for a rebalance operation. Possible values range from 1 to 11, with 11 being the fastest. If omitted, this value defaults to 11. The number of slaves for a rebalance operation is derived from the parallelization level specified in a manual rebalance command (POWER), or by the ASM_POWER_LIMIT parameter.
ASM_DISKSTRING is an operating system–dependent value used by ASM to limit the set of disks considered for discovery. When a new disk is added to a disk group, each ASM instance that has the disk group mounted must be able to discover the new disk using its ASM_DISKSTRING. If not specified, it is assumed to be NULL and ASM disk discovery finds all disks to which the ASM instance has read and write access.
ASM_DISK_GROUPS is the list of names of disk groups to be mounted by an ASM instance at startup, or when the ALTER DISKGROUP ALL MOUNT command is used.
Note: The internal packages used by ASM instances are executed from the LARGE POOL; therefore, you should set the value of the initialization parameter LARGE_POOL_SIZE to a value grater than 8 MB. For other buffer parameters, you can use their default values.

Monitoring Long-Running Operations Using V$ASM_OPERATION

The ALTER DISKGROUP DROP, RESIZE, and REBALANCE commands return before the operation is complete. To monitor progress of these long-running operations, you can query the V$ASM_OPERATION fixed view. This view is described in the table in this slide.

ASM File Types

ASM supports most file types required by the database. However, certain classes of file types, such as operating system executables, are not supported by ASM. Each file type is associated with a default template name.
This table specifies ASM-supported file types with their corresponding naming conventions.
When ASM creates a data file for a permanent tablespace (or a temp file for a temporary tablespace), the data file is set to auto-extensible with an unlimited maximum size and 100 MB default size. An AUTOEXTEND clause may override this default.
ASM applies attributes to the files that it creates as specified by the corresponding system default template.

Data Dictionary Changes

In an ASM instance, V$ASM_CLIENT contains one row for every database instance using a disk group managed by the ASM instance. In a database instance, it has one row for each disk group with the database name and ASM instance name.
In an ASM instance, V$ASM_DISKGROUP contains one row for every disk group discovered by the ASM instance. In a database instance, V$ASM_DISKGROUP has a row for all disk groups mounted or dismounted.
In an ASM instance, V$ASM_TEMPLATE contains one row for every template present in every disk group mounted by the ASM instance. In a database instance, it has rows for all templates in mounted disk groups.
In an ASM instance, V$ASM_DISK contains one row for every disk discovered by the ASM instance, including disks which are not part of any disk group. In a database instance, it has rows for disks in the disk groups in use by the database instance.
In an ASM instance, V$ASM_OPERATION contains one row for every active ASM long-running operation executing in the ASM instance. In a database instance, it contains no rows.
In an ASM instance, V$ASM_FILE contains one row for every ASM file in every disk group mounted by the ASM instance. In a database instance, it contains no rows.
In an ASM instance, V$ASM_ALIAS contains one row for every alias present in every disk group mounted by the ASM instance. In a database instance, it contains no rows.

© 2010, www.oracledatabase12g.com. 版权所有.文章允许转载,但必须以链接方式注明源地址,否则追究法律责任.

相关文章 | Related posts:

1. Extending Automatic Storage Management to Manage ALL DataOracle Database 11g Release 2
2. Oracle Database 11gr1/10gr2 Automatic Storage Management Overview and Technical Best Practices
3. Top 10 Things You Always Wanted to Know About Automatic Storage Management But Were Afraid to Ask
4. CLOBs and NCLOBs character set storage in Oracle Release 8i, 9i, 10g and 11g
5. ORA-1092 During Startup Using AUM (Automatic Undo Management)
6. Best Practices for Automatic Failover Using Oracle Data Guard 10g Release 2
7. Automatic PGA Memory Management
8. Pro Oracle Database 11g Administration
9. Expert Oracle Practices Oracle Database Administration from the Oak Table PDF
10. Automatic Memory Management(AMM) on 11g