This section explains the basic concepts and tasks involved in migrating data to and from Oracle ASM.
This section includes the following topics:
Alternatives to Oracle ASM storage include file systems, raw disks, and SAN configurations. Oracle ASM includes numerous benefits over these storage alternatives, including performance optimization, redundancy protection, and load balancing. You do not need a third-party Logical Volume Manager because Oracle ASM manages disks for you. Oracle Real Application Clusters (Oracle RAC) databases benefit from Oracle ASM because it provides ready-made shared storage.
If a database currently uses a storage system other than Oracle ASM, then you can migrate all or part of the database into Oracle ASM, thereby simplifying database administration. You can also migrate a fast recovery area to Oracle ASM.
Native operating system commands such as Linux cp or Windows COPY cannot write or read files in Oracle ASM storage. Because RMAN can read and write Oracle ASM files, you can use RMAN to copy data files into and out of Oracle ASM storage or between Oracle ASM disk groups. This technique is useful if you must store backups on user-managed disks.
You can migrate data to Oracle ASM with RMAN even if you are not using RMAN as your primary backup tool. The migration requires one RMAN database backup.
If you have sufficient disk space to hold the entire database both in Oracle ASM and alternative storage systems, then you can move a database directly into Oracle ASM. If you do not have sufficient storage, then you can back the database up to tape, create an Oracle ASM disk group that uses old disk space, and restore the database from tape to Oracle ASM.
After you set the location of the new recovery area, existing backups remain in the old recovery area and count against the total disk quota of the recovery area. The backups are deleted from the old recovery area when space is needed. These backups are usable by RMAN. It is not necessary to move legacy backups to the new Oracle ASM recovery area unless you need disk space. To free space consumed by files in the old recovery area, you can back them up to tape or migrate them to the Oracle ASM recovery area.
A foreign archived redo log is a log received by a logical standby database for a LogMiner session. Foreign archived redo logs cannot be migrated. Unlike normal archived logs, foreign archived logs have a different internal database identifier (DBID). For this reason, they cannot be backed up or restored on a logical standby database.
Migrating a database from Oracle ASM to an alternative storage system is similar to migration from an alternative storage system to Oracle ASM. The primary change is to modify each step to refer to file locations in the alternative storage system.
This section discusses the process of migrating the entire database and fast recovery area from alternative storage to Oracle ASM using RMAN.
The fast recovery area is an optional disk location that you can use to store recovery-related files such as control file and online redo log copies, archived redo log files, flashback logs, and RMAN backups. Oracle Database and RMAN manage the files in the fast recovery area automatically. You can specify the disk quota, which is the user-specified maximum size of the fast recovery area. When the disk quota is reached, Oracle automatically deletes files that are no longer needed.
Flashback logs are Oracle-generated logs used to perform flashback database operations. The database can only write flashback logs to the fast recovery area. Flashback logs are written sequentially and are not archived. They cannot be backed up to disk.
To migrate the entire database and fast recovery area from alternative storage to Oracle ASM, perform the following steps:
Back up the database and server parameter file, and disable Oracle Flashback Database.
The Oracle Flashback Database option returns the entire database to a prior consistent System Change Number (SCN) with the FLASHBACK DATABASE command in RMAN or SQL. A database flashback is different from traditional media recovery because it does not involve the restore of physical files, instead restoring your current data files to past states using saved images of changed data blocks. This feature uses flashback logs and archived redo logs.
This step is described in "Preparing to Migrate the Database to Oracle ASM Using RMAN".
Restore files to Oracle ASM, recover the database, and optionally migrate the fast recovery area to Oracle ASM.
This step is described in "Migrating the Database to Oracle ASM Using RMAN".
To migrate files from Oracle ASM to alternative storage, see "Migrating a Database from Oracle ASM to Alternative Storage".