Chapter 9. Understanding Automatic Storage Management
ORACLE DATABASE 10G: ADMINISTRATION II EXAM OBJECTIVES COVERED IN THIS CHAPTER:
Set up initialization parameter files for ASM and database instances.
Execute SQL commands with ASM filenames.
Start up and shut down ASM instances.
Administer ASM disk groups.
Use RMAN to migrate your database to ASM.
NOTE
Exam objectives are subject to change at any time without prior notice and at Oracle's sole discretion. Please visit Oracle's Training and Certification website (http://www.oracle.com/education/certification/) for the most current exam objectives listing.
One of the biggest enhancements introduced in Oracle Database 10g (Oracle 10g) is Automatic Storage Management (ASM). ASM is a cluster file system that can be used either with stand-alone Oracle instances or with Oracle Real Application Clusters (RAC) to provide a vertically integrated subsystem encapsulating a file system, a volume manager, and a fault-tolerant environment specifically designed for Oracle databases. It works in concert with other Oracle features such as Oracle Managed Files (OMF) to not only make disk space management easier but also to enhance the performance of the database by automatically spreading the I/O load across all available hardware devices.
As with most features of Oracle 10g, Oracle Enterprise Manager (EM) Database Control provides wizards and a graphical interface for ASM, making it easy to leverage ASM features when the command-line syntax is unfamiliar or difficult to remember.
When creating a new tablespace or other database structure such as a control file or redo log file, you can specify a structure new to Oracle 10g called an ASM disk group as the storage area for the database structure instead of an operating system file. ASM takes the ease of use of OMF and combines it with mirroring and striping features to provide a robust file system and logical volume manager that can even support multiple nodes in an Oracle RAC. ASM eliminates the need to purchase a third-party logical volume manager. To provide further benefits beyond a typical third-party logical volume manager, ASM stripes files, not logical volumes.
In this chapter, we will delve further into the architecture of ASM. In addition, we will show you how to create a special type of Oracle instance to support ASM as well as how to start up and shut down an ASM instance. We will describe the new initialization parameters related to ASM and the existing initialization parameters that have new values to support an ASM instance. In addition, we will explain the variety of methods that you can use to refer to an ASM filename. A number of new dynamic performance views support ASM, providing different functionality depending on whether they reside in the ASM instance or in the traditional RDBMS instance. Also, we will use some raw disk devices on a development Linux server to demonstrate how disk groups are created and maintained. Finally, we will show you how to migrate your entire database to an ASM environment.