SAP Note 964619 RMAN: Incremental backups with Block Change TrackingNote Language: English Version: 15 Validity: Valid Since 31.01.2011 The displayed SAP Note is not up to date in the selected language / Summary Symptom Fast incremental database backups with RMAN This note describes how Block Change Tracking (BCT) can be used to make incremental database backups with Recovery Manager (RMAN) faster. RMAN Block Change Tracking is available as of Oracle Release 10.2. This note is valid for Oracle Releases 10.2 and 11.2. Other terms Fast incremental Backup Fast incremental Backup on Physical Standby Reason and Prerequisites Use of "Fast Incremental Backup" with SAP New with Oracle ASM During ASM installations, the Oracle Block Change Tracking File in ASM is stored under '+DATA/<DBSID>/bctf<DBSID>.ora' (see 'Configuration' below). New with Oracle release 11.2: "Fast incremental Backup on Physical Standby" As of Oracle Release 11g, Block Change Tracking can also be activated in the standby database to reduce the burden on the primary database. To use 'Fast Incremental Backup on Physical Standby', you require a license for the 'Oracle Active Data Guard' option. New with Oracle release 10.2: "Fast incremental Backup" Solution Contents of this note Block Block Block Block Block Change Change Change Change Change Tracking Tracking Tracking Tracking Tracking - Description Configuration Support by SAP BR*Tools Recommendations Administration Page 1 of 8 13.12.2011 which is described below.Description Block Change Tracking (Abbreviated: BCT) is a new RMAN function as of Oracle database 10g (Enterprise Edition). by default. This means that an incremental backup (level 1) using Oracle9i takes just as long as a complete backup (level 0). When you activate BCT for the first time. RMAN must read all blocks for each data file during the first level 0 backup. Oracle uses the Block Change Tracking File ( BCTF) book to list which data blocks have changed since the last RMAN level 0 backup.Configuration BCTF default storage location during SAP installations <DBSID> = Database name o For file systems on Unix/Linux platforms '<ORACLE_HOME>/dbs/bctf<DBSID>.12. the duration is proportional to the number of changed blocks. RMAN must read all of the blocks of a datafile (including those that have not changed) during an incremental backup. Block Change Tracking is deactivated. However. Performance improvement due to Block Change Tracking: The duration of an incremental backup is approximately proportional to the size of the database. For each database. there is a block change tracking file. a maximum of eight incremental backups that use this feature can be performed. If BCT is activated. after a level 0 backup. since the BCTF does not reflect the actual current block status when it is first created. RMAN then uses the information from the BCTF in incremental backups to read and backup only those blocks that have been changed. block change tracking saves a very large amount of time. Block Change Tracking . an additional configuration is required. The BCTF is written by the new Oracle background process CTWR.SAP Note 964619 RMAN: Incremental backups with Block Change Tracking Block Change Tracking . If you perform more than eight incremental backups between two level 0 backups.ora' o For file systems on Windows platforms Page 2 of 8 13.2011 . you must note that. By default. When block change tracking is active. in order to identify the blocks that have changed since the last full backup. Up to Oracle 9i (inclusive). if BCT is deactivated. Block Change Tracking (BCT) notably decreases the time required for incremental backups using RMAN. If only a small portion of the blocks changes between two level 0 backups. RMAN can only use the information from the BCTF in the subsequent incremental backups. Recommendations Note the following recommendations for using BCT: o Only activate Block Change Tracking if you perform incremental Page 3 of 8 13.SAP Note 964619 RMAN: Incremental backups with Block Change Tracking '<ORACLE_HOME>\DATABASE\bctf<DBSID>.00 patch level 15 Configuration of the SAP BR*Tools For Block Change Tracking. This subsequent cataloging does not initialize the BCTF. The creation and deletion is carried out using the database.2 or higher SAP BR*Tools as of SAP Release 7. or manage the Block Change Tracking File.ora' Block Change Tracking is activated SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '<location>' REUSE. BR*Tools do not save. Block Change Tracking . so that you can use it as a reference backup for subsequent incremental RMAN backups. Set one of the following parameters in the BR*Tools profile file init<DBSID>. create.sap for an incremental backup strategy using RMAN with BR*Tools: o o o backup_dev_type = rman_util|rman_disk|rman_stage tape_copy_cmd = rman disk_copy_cmd = rman For further information.12. To initialize the Block Change Tracking File (and therefore activate Block Change Tracking). you must carry out a genuine RMAN level 0 backup using RMAN.ora' o With Automatic Storage Management (ASM) '+DATA/<DBSID>/bctf<DBSID>.Support by SAP BR*Tools Block Change Tracking is supported in the SAP environment with the following prerequisites: o o Oracle Database Release 10. Block Change Tracking .sap does not have to be changed. the profile file init<DBSID>. refer to the SAP BR*Tools documentation on SAP Service Marketplace. Subsequent cataloging of RMAN backups BR*Tools also provides you with the option of cataloging a non-RMAN backup of the database as a level 0 RMAN backup.2011 . 1) Block Change Tracking . For example: For example. SQL> SELECT count(1) from v$backup_datafile where used_change_tracking = 'NO'. A bitmap that contains space for seven incremental backups before the space is overwritten is sufficient for this type of backup strategy. for some reason. if your backup strategy assumes that more than seven incremental backups take place between two level 0 backups.2011 Page 4 of 8 . you must set the parameter _bct_bitmaps_per_file to a higher value to ensure that the relevant number of bitmaps is available to save the Block Change Tracking information and to ensure that all incremental backups can take advantage of Block Change Tracking.1. We therefore recommend that you regularly check the status of the BCTF and its use for backups. the database cannot access the BCTF. o Parameterization of _bct_bitmaps_per_file A normal backup strategy performs a level 0 backup (full backup) once a week and performs an incremental backup on the other days. However. If you determine that certain incremental backups on certain days run for significantly longer than those on other days. The Block Change Tracking file allocates more space accordingly but this does not affect performance. (Oracle MetaLink Notes: 745798. o Regular monitoring If.12. if you perform a level 0 backup only once per month but you perform an incremental backup daily.SAP Note 964619 RMAN: Incremental backups with Block Change Tracking backups using RMAN. you must check whether these backups are using BCT and increase the parameter _bct_bitmaps_per_file if required. Deactivating Block Change Tracking SQL> ALTER DATABASE DISABLE BLOCK CHANGE TRACKING. the following configuration would be useful: SQL> alter system set "_bct_bitmaps_per_file" = 32.Administration Activating Block Change Tracking SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '<location>' REUSE. 13. 452455. Block Change Tracking is automatically deactivated. This deactivates BCT and deletes the BCTF from the file system. Stopping background process CTWR Deleted file /oracle/QO1/112_64/dbs/bctf. Shut down the database SQL> shutdown immediate Copy the BCTF from the file system to the new storage location Mount the database SQL> startup mount Rename the BCTF in the database SQL> ALTER DATABASE RENAME FILE '<path_old>' TO '<path_new>'. o 1.SAP Note 964619 RMAN: Incremental backups with Block Change Tracking Block Change Tracking Status Monitoring SQL> COLUMN STATUS FORMAT A8 SQL> COLUMN FILENAME FORMAT A60 SQL> select status.. Open the database: SQL>ALTER DATABASE OPEN.12. OS id=15775 Block change tracking service is active. Block Change Tracking status in the alert log The alert log also displays the current BCT status: o At activation: . Mon Jan 03 13:44:13 2011 alter database enable block change tracking using file '?/dbs/bctf. filename from V$BLOCK_CHANGE_TRACKING. Determine the current storage location of the BCTF SQL> SELECT filename FROM V$BLOCK_CHANGE_TRACKING. At deactivation: .. Starting background process CTWR Mon Jan 03 13:44:13 2011 CTWR started with pid=47. Completed: alter database enable block change tracking using file '?/dbs/bctf. 6.. the information is retained in the BCTF... 3... Page 5 of 8 2. 5.2011 .dbf Completed: alter database disable block change tracking ..dbf' Block change tracking file is current. Renaming the BCTF When you rename the BCTF. 4.dbf' . Mon Jan 03 14:19:59 2011 alter database disable block change tracking Mon Jan 03 14:19:59 2011 Block change tracking service stopping. 13. For this reason. Execute a new level 0 backup. Procedure after Restore/Recovery: After a Restore/Recovery.2: The use of Block Change Tracking in the standby database is not supported.2: "Fast incremental Backup on Physical Standby" The use of Block Change Tracking in the standby database is supported by Oracle. The BCTF is a binary file. Deactivate BCT. Block change tracking and physical standby databases Oracle Release 11. Additional processing load caused by Block Change Tracking: Use the following rule of thumb to estimate the size of the Block Change Tracking File for a single instance system: S_BCTF [MByte] = S_DB * 10 [MByte] S_BCTF: Size of the Block Change Tracking File in megabytes. Deactivate Block Change Tracking SQL> ALTER DATABASE DISABLE BLOCK CHANGE TRACKING. but it has no effect on incremental RMAN backups. you must recreate the BCTF.12. It is possible to activate Block Change Tracking on the standby side of a physical standby database.further information: Changes to the block change tracking status are logged in the alert log. 1. Block Change Tracking . 1. Prerequisite: 'Oracle Active Data Guard' Oracle Release 10. the current Block Change Tracking information is lost. 2.2011 Page 6 of 8 . It is not saved. The BCTF is automatically extended as required when the database expands. S_DB : Size of the database in terabytes. So the BCTF for a 3TB database will occupy approximately 30MB. 3. Activate Block Change Tracking again SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '<path_new>'. 2.SAP Note 964619 RMAN: Incremental backups with Block Change Tracking Deactivating and reactivating BCT During deactivation and reactivation. This procedure is a part of the BRRECOVER function. Reactivate BCT. we recommend that you not activate BCT on a standby database. After reestablishing a database 13. the BCTF will occupy approximately 3 * 4 * 10 = 120MB.SAP Note 964619 RMAN: Incremental backups with Block Change Tracking (using Restore/Recovery). the system automatically creates the BCTF again the next time the instance is restarted.2011 Page 7 of 8 . Block Change Tracking and Real Application Clusters (RAC) Use the following rule of thumb to estimate the size of the Block Change Tracking File for RAC systems: S_BCTF [MByte] = S_DB * N_RAC * 10 [MByte] S_BCTF: Size of the Block Change Tracking File in megabytes. If the BCTF is missing. which can be accessed by all nodes of the cluster and by all RAC instances.1) to check if the BCTF has been used in an RMAN backup: SELECT FILE#. the Block Change Tracking File must be on a single hard drive. V$BACKUP_DATAFILE contains a column called USED_CHANGE_TRACKING.12.2011 09:34:05 German Recommendations/additional info Consulting BC-DB-ORA Oracle 13. AVG(BLOCKS_READ). AVG(BLOCKS_READ/DATAFILE_BLOCKS) * 100 AS "% READ FOR BACKUP" FROM V$BACKUP_DATAFILE WHERE INCREMENTAL_LEVEL > 0 AND USED_CHANGE_TRACKING = 'YES' GROUP BY FILE# ORDER BY FILE#. AVG(DATAFILE_BLOCKS). Header Data Release Status: Released on: Master Language: Priority: Category: Primary Component: Secondary Components: BC-DB-ORA-DBA Database Administration with Oracle Released for Customer 29. If this column contains the value 'YES' for an incremental backup (incremental_level > 0) means that RMAN has used the BCTF. S_DB : Size of the database in terabytes. N_RAC : Number of RAC instances. In an Oracle-RAC environment. even though block change tracking is activated. you must recreate the BCTF. So for a 3 terabyte database with 4 RAC nodes. You can use the following query (refer to metalink Note 262853.09. SAP Note 964619 RMAN: Incremental backups with Block Change Tracking The Note is release-independent Related Notes Number 842240 828268 619188 105047 Short Text FAQ: Backup strategy of large and highly-available databases Oracle Database 10g: New functions FAQ: Oracle wait events Support for Oracle functions in the SAP environment Attributes Attribute Database system Value ORACLE 13.12.2011 Page 8 of 8 .