Showing posts with label RMAN. Show all posts
Showing posts with label RMAN. Show all posts

Tuesday, July 25, 2017

Oracle Recovery Manager Features: BACKUP AS COPY

What is the advantage backup as copy feature in RMAN?

RMAN(Recovery Manager) utility creates backup in the form of backupsets or backup pieces by default.RMAN utility also allows other method which is similar to user managed hot backup. It can be acheived using 'BACKUP AS COPY' command.Using "Backup as Copy" RMAN creates backup in the form of image copies. However, we do not need to put the database in begin backup/end backup mode as in Conventional Hot Backup.

Syntax for Datafile Backup using Backup as copy:

RMAN> backup as copy datafile 1 format '/backup/data/datafile01.dbf' ;



Another advantage of this feature is that it allows to create image copy of control file.

 RMAN> backup as copy current controlfile format 'F:\CntrlFile_Bkp.ctl';  


How do we identify backups taken  as Image copies using RMAN?

Use "LIST COPY" Command. "LIST BACKUP" only gives a list of backup sets which were created using default RMAN backup Methos.

Syntax:

RMAN> LIST COPY;

Thursday, July 06, 2017

How to Configure RMAN Backups into Multiple Locations?

If we need  RMAN to distribute backup sets among multiple disks on different mountpoints. We can use the below syntax to configure backup in multiple locations.

Using Allocate Channel:

RUN
{
ALLOCATE CHANNEL c1 DEVICE TYPE DISK FORMAT '/u01/oracle/data1'; 
ALLOCATE CHANNEL c2 DEVICE TYPE DISK FORMAT '/u02/oracle/data2'; 
}

Using Configure Channel:

CONFIGURE CHANNEL DEVICE TYPE DISK FORMAT '/u01/%U', '/u02/%U';

Tuesday, June 27, 2017

Oracle RMAN (Recovery Manager) Concepts

What is the difference between obsolete and expired Backup in RMAN?

Obsolete Backup: Backup pieces or backup sets which are not needed for recovery.
We can use the REPORT OBSOLETE command to list the obsolete backups and DELETE OBSOLETE command to delete the obsolete backup.

Expired Backup:When the CROSSCHECK command is used to determine whether backups recorded in the repository still exist on disk or tape, if RMAN cannot locate the backups, then it updates their records in the RMAN repository to EXPIRED status.We can then use the DELETE EXPIRED command to remove records of expired backups from the RMAN repository.

Friday, May 05, 2017

Oracle Database Administrator Interview Questions on RMAN

RMAN INTERVIEW QUESTIONS
========================

1.What is the difference between recovery catalog and Nocatalog backup in RMAN?

NoCatalog Backup:

ByDefault RMAN connects to the target database in Nocatalog Mode.
In Nocatalog Mode, Backup Information and Metadata related to RMAN is stored in target database controlfile.

Catalog Backup:

A recovery catalog is a schema created in a separate database that contains metadata obtained from the target control file.
In recovery catalog we can store rman scripts.

We can store metadata about multiple incarnations of a single target database in the catalog.
Recovery catalog is central and can have information of many databases.
If the control file is lost and must be restored from backup, the backup configuration information is available when the database is not mounted.

2.What are the differences between crosscheck and validate commands?

Validate command is to examine a backup set and report whether it can be restored. RMAN scans all of the backup pieces in the specified backup sets and looks at the checksum to verify that the contents are intact so that backup can be successfully restored if necessary.

Crosscheck command is to verify the status of backups and copies recorded in the RMAN repository against media such as disk or tape. The crosscheck command only processes files created on the same device type as the channel running crosscheck.

3.What is obsolete backup & expired backup?

A status of “expired” means that the backup piece or backup set is not found in the backup destination.

A status of “obsolete” means the backup piece is still available, but it is no longer needed. The backup piece is no longer needed since RMAN has been configured to no longer need this piece after so many days have elapsed, or so many backups have been performed.

4.What is the difference between hot backup & RMAN backup?

We need to put the database in Backup mode for Hot  Backup. RMAN Backup does not need the database to be in Backup mode.

5. Which Tables are have information required for RMAN list & report commands ?
 V$BACKUP_FILES and recovery catalog views e.g.,  RC_DATAFILE_COPY or RC_ARCHIVED_LOG.

Below tables contain RMAN Catalog information:

RC_DATABASE_INCARNATION 
RC_BACKUP_COPY_DETAILS
RC_BACKUP_CORRUPTION
RC_BACKUP-DATAFILE_SUMMARY




Thursday, March 24, 2016

Oracle RMAN Inremental Backup Algorithm and Change Tracking File

During an incremental backup, RMAN reads the SCN of each data block in the input file and compares it to the checkpoint SCN
of the parent incremental backup. If the SCN in the input data block is greater than or equal to the checkpoint SCN of the
parent, then RMAN copies the block.


Performance of incremental Backup can be improved by enabling block change tracking.When Change tracking is enabled, all the changes to datablocks are recored in change tracking file. RMAN can read the changed SCN's from change tracking file, instead of reading each and every input file.
One change tracking file is created for the entire database.
By default, the change tracking file is created as an Oracle managed file in DB_CREATE_FILE_DEST. We can specify the name of the block change tracking file by providing the location you choose.


SQL command to enable block change tracking

SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING;
This creates change tracking file in "db_create_file_dest" directory


SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING  USING FILE '/test1/data/rman_change_track.f' REUSE;
This creates the change tracking file in the location specified.


SQL command to disable block change tracking

SQL> ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;
By Default,  block change tracking is disabled.
If the change tracking feature is disabled, any existing change tracking files will be deleted


SQL query to find change tracking file Details

select filename, status from v$block_change_tracking


How to Relocate the change tracking file


1.Shut down the database

SHUTDOWN IMMEDIATE

2.Using OS commands, move the change tracking file to a new location.

3.Mount the database and move the change tracking file to a location that has more space.

SQL query to rename change tracking file

ALTER DATABASE RENAME FILE   '/test1/data/rman_change_track.f' TO '/newtest1/data1/change_trk.f';

4.Open the database:

ALTER DATABASE OPEN;


If we cannot afford downtime for database shutdown, change tracking file can be relocated as below


ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;
ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE 'new-location';

Contents of change tracking file will be lost if we use the above method.So its not a preferable method.
RMAN will have to scan the entire file until the next level 0 incremental backup is done