Oracle Recovery Manager (RMAN) is the main tool used in restoration of databases, tables, records, Meta data attributes, queries, triggers, stored procedures and other objects in the oracle database. The task of working with these complex procedures is best handled when it is handed over to the database administrators or a qualified professional. We have a team of experts who have practical experience in handling many corporate level RDBMS (Relational Database Management Systems) like Oracle, SQL server, Ingres, MySQL and others. They can work closely in coordination with your database administration team and users to solve most of the disaster recovery problems with corrupt or damaged Oracle database systems.
Client server scenario
Whenever you think of Oracle database systems, always remember the client server scenario wherein Oracle client from the workstation interacts with the server application and database engine in the database server computer.
RMAN: – Oracle Recovery Manager Client is the one which always interprets the commands related to backup and recovery procedures. It is responsible for passing commands into the currently running server sessions from the client systems. The server session recognizes these commands from RMAN and executes them. Whenever a database is set for backup or recovery, RMAN issues a command to record all the activities associated with them in the target database within the control file.
Components: – Apart from RMAN, the database recovery environment in Oracle uses three other components that are optional in nature. They are the catalog, media software and flash recovery area.
The recovery catalog is in fact a database in which a unique schema is utilized for recording all sorts of activities initiated by RMAN, performed on single or multiple database files. Media management is software which acts as an interface between RMAN and backup/restore devices such as tape drives external USB drives etc. Flash recovery area is a location within the disk area where files related to backup/recovery are stored.
Oracle recovery process considers many basic terms like target database, repository, client, catalog, recovery area, media manager and channels.
It could be the backup database, recovery database or restoring database which depends on the nature of task being executed.
If you have worked on SQL+ commands, you will be able to correlate them with RMAN commands. The technician will be able to work with RMAN commands as well as SQL+ commands from the RMAN client application which communicates with the Oracle server processes which are directed towards the target databases. The other way in which RMAN can be used is through the Enterprise manager utility available in the Oracle system.
Control files in the target database are maintained in the repository. Database schema, configuration details, commit and rollback settings and other objects related to the target database are also stored in the repository area.
The database recovery-catalog is another file in which the repository details are stored in the system. This will be used by RMAN to control and monitor the recovery procedures in case of control files deletion. The catalog also holds stored procedures which are sequences of RMAN and SQL+ commands used for data recovery and backup procedure management. This is said to be more convenient than working with commands, since the stored procedures stay at the target database and get executed within the server space, while the SQL commands will have to pass the control from the client to the server.
Flash recovery area
This is the region where disk space management and file handling procedures are featured, in relation to the procedures related to recovery and back up. The technician will be able to initialize the recovery by issuing the commands DB_RECOVERY_FILE_DEST and DB_RECOVERY_FILE_DEST_SIZE. These two commands help in optimization of backup and recovery processes.
It is in fact a software application which is responsible for monitoring and controlling the activities related storage and backup devices.
Channels are the Input /Output paths for the backup and restore operations. They are configured by RMAN with the help of CONFIGURE commands.
Initialization of RMAN
RMAN is initialized with the command
Oracle offers three basic modes of recovery namely complete database recovery, current table spaces, current data files and data blocks. When the technician opts for complete database recovery, he will be able to restore all the objects within the database from the point of latest backup that has been taken.
By keeping the database open it is possible to recover only specific table names that have corrupted. Options for the recovery of multiple tables also exist within single or multiple database files. Oracle RMAN also offers options for recovering single or multiple table spaces to be recovered from a single database or multiple databases.
Disk space corrections
In some cases the disk drive in the server or client system may be corrupt due to bad sectors when accessibility to the database may be denied. In such cases you need to set right these issues before taking any steps to recover Oracle databases. If your HDD is corrupt due to logical or physical damages then you need to go for scanning and fixing them by adopting specific procedures.
The three methods of disk repair ate drive-restoration, disk-imaging and data-salvaging. Hardware tools like platter exchange, head exchange, magnet fixing, motor fixing, and HDD component alignment tools are used restore the drive and its components in the first stage. The second stage involves mirroring of data from failed disk onto another “good disk” as it is. All the data from repaired sectors get mirrored into the target disk. Data from unrepaired sectors in the source disk may get mirrored partially. This process completes the second stage. In the third stage you need to use a data recovery software tool for regrouping and repairing files. Make sure that you select a tool that can fix MBR errors also. It is always better to let the system perform a complete scan before fixing the files. Auto repair and data recovery tools provide best of solutions for maximum data recovery.