Overview
The types of Oracle files that should be included in an EVM-Oracle job vary with the tasks to be performed. The following recommendations apply to backups of active, online databases.
The EVM-Oracle backup plan for online databases should include:
Tablespaces and data files
Archived redo log files
Control file
init.ora file
Selecting Tablespaces and Data Files
An Oracle database contains tablespaces, which are logical entities that contain one or more data files. Data files are physical files which can be distributed over multiple storage units (see example below).
For each database, Oracle initially creates System and User tablespaces. Other tablespaces and data files can be added to the database over time, creating a dynamic situation that can complicate backup planning. Thus, it is important to understand the relationship between a tablespace and the location of its data files on the StorageWorks subsystem.
IMPORTANT: When creating an EVM job to replicate a tablespace that spans multiple storage units, you must include each unit that contains a portion of the tablespace.
Example
Suppose you want to replicate portions or all of a database which contains the tablespaces System, User, Temp and Web. The tablespaces and their associated data files are located as follows:
Tablespace |
/west (unit D1) Data files |
/east (unit D2) Data files |
/central (unit D3) Data files |
System | System_ora1.ora | System_ora2.ora | - |
User | User_ora1.ora | User_ora2.ora | - |
Temp | Temp_ora1.ora | - | - |
Web | Web_ora1.ora | Web_ora2.ora Web_ora3.ora |
Web_ora4.ora Web_ora5.ora |
To replicate the System and User tablespaces, you would specify replication of directories /west (unit D1) and /east (unit D2) in the EVM job. To replicate Temp, the job must include /west (unit D1). To replicate Web, the job must include directories /west (unit D1), /east (unit D2) and /central (unit D3).
Omitting Online Redo Log Files from Backup Jobs
Oracle redo logs contain information that can be used during recovery of a database to apply changes that were not written to disk due to a failure event. Each redo log file is identified by a sequence number.
At least two online redo logs are always maintained. Often, multiple copies are maintained on separate physical disks. When using the online backup feature, Oracle also maintains an archived redo log, which is an exact duplicate of each online redo log. For backup jobs, you should specify archived redo log files, not online redo log files. Restoring an online redo log file will overwrite the active, online redo log and make it impossible to completely recover the database.
IMPORTANT: For backup jobs, do not include online redo log files.
Selecting Archived Redo Logs
When using the archivelog command to enable online backup, Oracle creates archived redo log files by copying the online redo logs to the location specified by the archive_log_dest parameter in the init.ora file.
Oracle may archive some redo logs after the EVM-Oracle job has replicated the tablespaces. You must copy these logs to ensure that all required redo logs accompany the tablespaces. You can do this by running a separate EVM-Oracle job or by copying the files outside of EVM.
IMPORTANT: Include all required redo logs. Any gap in the archived redo log sequence will prevent complete recovery.
Selecting the Control File
The database control file is a small but critically important administrative file that contains the names, locations and status of all data files and redo logs. You should follow Oracle's recommended procedures for including control files with backups.
In particular, if a control file is located on the same source unit as the data files, it should not be backed up with the data files. If it is backed up, it must not be restored because it will overwrite the active control file, causing an incomplete restore and loss of data.
Selecting the init.ora File
The init.ora file is a small administrative file that contains system parameters that are used during database startup. It is a critical file that should be backed up with the control file.