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Oracle Disk I/O Tuning

Chapter 5:

ASM Disk Groups

A disk group is basically one or more ASM disks that are managed as a single logical unit. Any data-structure stored in an ASM disk group is totally contained within that disk group, or self-contained. A database using ASM disks doesn't have to be shutdown in order for a disk to be added or dropped. ASM rebalances the spread of data to ensure an even I/O load to all disks in a disk group when the disk group configuration changes.

We mentioned that any single ASM file is self-contained in a single ASM disk group. However, an ASM disk group can contain files belonging to several databases, and a single database can use storage from multiple ASM disk groups.  You can specify a disk group as the default disk group for files created in a database by specifying the disk group in file destination initialization parameters. 

ASM divides files into 1MB extents and spreads the extents for each file evenly across all of the disks in a disk group. ASM uses pointers to record extent location instead of using a mathematical function to track the placement of each extent. When the disk group configuration changes, ASM moves individual extents of a file rather than having to move all extents to adhere to a formula based on the number of disks.

The above text is an excerpt from:

Oracle Disk I/O Tuning
Disk IO Performance & Optimization for Oracle Databases



by Mike Ault

Oracle Consulting Services

Burleson Oracle Consulting offers Senior Oracle consultants which are available for all areas of Oracle support.  Common Oracle consulting support activities include short-term Oracle tuning, Oracle database troubleshooting, Oracle9i and Oracle10g migration, Oracle9iAS App Server consulting, Oracle design reviews and Oracle requirements evaluation support. Oracle support and Oracle consulting services are priced by the hour, so you only pay for what you need. These one-time Oracle consulting services commonly include:

  • Answering questions from your Oracle DBA technical staff

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