Availability and Recovery - RMAN Improvements
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Oracle Database 10g comes with a plethora of improvements (I like that word, plethora!) for RMAN. These include the following:
- Using flash recovery area
- Using backup copies and fast recovery
- Using the catalog and uncatalog commands
- Dropping a database in RMAN
- Unregistering a database in RMAN
- Making and using RMAN backup copies
- Configuring default disk backup types
- Changes to incremental backups
- Recovering datafiles not backed up
- Changes in error reporting
- Compressing RMAN backups
- Using RMAN-related tablespace point-in-time related recovery changes
Using the Flash Recovery Area
Oracle Database 10g offers the flash recovery area, which allows you to centralize storage of all recovery-related files. The flash recovery area is an area of disk that is defined for use for recovery-related files. The flash recovery area can use locally attached storage, Clustered File Systems, or Oracle Database 10g’s new Automatic Storage Management (ASM) features.
Table 5-1 lists the file types that are backed up within the flash recovery area.
Why Use the Flash Recovery Area?
The flash recovery area helps with the management of overall disk space allocation and provides a centralized storage area for all related recovery files. It provides for much faster backup and restore operations as well. The flash recovery area is created in a specific location (defined by a file system, or use of ASM). You define the maximum size of the flash recovery area via database parameters. As files are added or removed from the flash recovery area, records of these events are logged in the database alert log. You can check the new DBA view, DBA_ OUTSTANDING_ALERTS, for information on outstanding issues with the flash recovery area, as shown in this example:
Select * from dba_outstanding_alerts;
File Type | Notes |
Control file | One copy of the control file is created in the flash recovery area when the database is created. |
Archived redo logs | When you configure the flash recovery area (as described later in this section), the parameter log_archive_dest_10 is automatically configured, and archived redo logs are archived to that destination, as well as any other archive log destinations. |
Flashback logs | Flashback logs (discussed later in this chapter) are stored in the flash recovery area, if it is defined. |
Control file autobackups | The default location for the RMAN control file autobackups is the flash recovery area, if it is defined. |
RMAN datafile copies | The default location for the RMAN datafile copies is the flash recovery area, if it is defined. |
RMAN backup and other related files | The default location for the RMAN files in general (backup-set pieces, etc.) is the flash recovery area, if it is defined. |
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TABLE 5-1.
File Types Backed Up Within the Flash Recovery Area Jonathan Says… I really like the basic concept of the flash recovery area. Disks are much too big these days, and the most important thing you can do with big disks is find a good excuse for not using more than about 10GB per disk as “active space.” In the past I have advised people to take a couple of generations of backup to disk (then copy to tape) as one way of restricting the amount of “real” data stored per disk. Now it’s legal! (Of course, I did have other, more official-sounding arguments in favor of this strategy.) |
Retention for files in the flash recovery area is determined by the RMAN retention policy. This is set via the RMAN
configure retention policy command, a feature which is in and of itself not new in Oracle Database 10g. If a file does not have a retention policy associated with it, or it’s a permanent file, then it will never be deleted. If a file is not yet obsolete under the RMAN retention policy, then it will not be deleted. Finally, archived logs are eligible for deletion once they are obsolete.
Once the amount of space in the flash recovery area starts to reduce to unsafe levels, Oracle Database 10g issues a warning to the alert log (at 90 percent used and at 95 percent used). Also, when there is less than 10 percent free space available in the flash recovery area, Oracle Databse 10g removes files that are on the obsolete file list.
NOTE-- Running out of space in the flash recovery area can be troublesome if that area is your only archive log destination, as this can cause your database to eventually halt. If the flash recovery area is to be your only archive log destination, monitor space availability carefully.
 This chapter is from Oracle Database 10g New Features, by Robert Freeman (McGraw-Hill/Osborne, 2004, ISBN: 0072229470). Check it out at your favorite bookstore today. Buy this book now.
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