1. What is RMAN ?
Recovery Manager (RMAN) is a utility that can manage your entire Oracle backup and recovery activities.
Which Files must be backed up?
Database Files (with RMAN)
Control Files (with RMAN)
Offline Redolog Files (with RMAN)
INIT.ORA (manually)
Password Files (manually)
2. When you take a hot backup putting Tablespace in begin backup mode, Oracle records SCN # from header of a database file. What happens when you issue hot backup database in RMAN at block level backup? How does RMAN mark the record that the block has been backed up ? How does RMAN know what blocks were backed up so that it doesn't have to scan them again?
In 11g, there is Oracle Block Change Tracking feature. Once enabled; this new 10g feature records the modified since last backup and stores the log of it in a block change tracking file. During backups RMAN uses the log file to identify the specific blocks that must be backed up. This improves RMAN's performance as it does not have to scan whole datafiles to detect changed blocks.
Logging of changed blocks is performed by the CTRW process which is also responsible for writing data to the block change tracking file. RMAN uses SCNs on the block level and the archived redo logs to resolve any inconsistencies in the datafiles from a hot backup. What RMAN does not require is to put the tablespace in BACKUP mode, thus freezing the SCN in the header. Rather, RMAN keeps this information in either your control files or in the RMAN repository (i.e., Recovery Catalog).
3. What are the Architectural components of RMAN?
1.RMAN executable
2.Server processes
3.Channels
4.Target database
5.Recovery catalog database (optional)
6.Media management layer (optional)
7.Backups, backup sets, and backup pieces
4. What are Channels?
A channel is an RMAN server process started when there is a need to communicate with an I/O device, such as a disk or a tape. A channel is what reads and writes RMAN backup files. It is through the allocation of channels that you govern I/O characteristics such as:
Type of I/O device being read or written to, either a disk or an sbt_tape
Number of processes simultaneously accessing an I/O device
Maximum size of files created on I/O devices
Maximum rate at which database files are read
Maximum number of files open at a time
5. Why is the catalog optional?
Because RMAN manages backup and recovery operations, it requires a place to store necessary information about the database. RMAN always stores this information in the target database control file. You can also store RMAN metadata in a recovery catalog schema contained in a separate database. The recovery catalog
schema must be stored in a database other than the target database.
6. What does complete RMAN backup consist of ?
A backup of all or part of your database. This results from issuing an RMAN backup command. A backup consists of one or more backup sets.
7. What is a Backup set?
A logical grouping of backup files -- the backup pieces -- that are created when you issue an RMAN backup command. A backup set is RMAN's name for a collection of files associated with a backup. A backup set is composed of one or more backup pieces.
8. What is a Backup piece?
A physical binary file created by RMAN during a backup. Backup pieces are written to your backup medium, whether to disk or tape. They contain blocks from the target database's datafiles, archived redo log files, and control files. When RMAN constructs a backup piece from datafiles, there are a several rules that it follows:
A datafile cannot span backup sets
A datafile can span backup pieces as long as it stays within one backup set
Datafiles and control files can coexist in the same backup sets
Archived redo log files are never in the same backup set as datafiles or control files RMAN is the only tool that can operate on backup pieces. If you need to restore a file from an RMAN backup, you must use RMAN to do it. There's no way for you to manually reconstruct database files from the backup pieces. You must use RMAN to restore files from a backup piece.
9. What are the benefits of using RMAN?
1. Incremental backups that only copy data blocks that have changed since the last backup.
2. Tablespaces are not put in backup mode, thus there is noextra redo log generation during online backups.
3. Detection of corrupt blocks during backups.
4. Parallelization of I/O operations.
5. Automatic logging of all backup and recovery operations.
6. Built-in reporting and listing commands.
10. Difference between catalog and nocatalog?
Ans : the difference is only who maintains the backup records like
when is the last successful backup incremental differential etc.
In CATALOG mode another database (TARGET database) stores all the information.
In NOCATALOG mode controlfile of Target database is responsible.
12. Difference between using recovery catalog and control file?
When new incarnation happens, the old backup information in control file will be lost. It will be preserved in recovery catalog.
In recovery catalog, we can store scripts.
Recovery catalog is central and can have information of many databases.
13. Can we use same target database as catalog?
No. The recovery catalog should not reside in the target database (database to be backed up), because the database can't be recovered in the mounted state.
14. How do u know how much RMAN task has been completed?
By querying v$rman_status or v$session_longops
15. From where list & report commands will get input?
16. Command to delete archive logs older than 7days?
RMAN> delete archivelog all completed before sysdate-7;
17. How many days backup, by default RMAN stores?
We have to specify the retention policy for that...using
RMAN>configure rentention policy for the recovery window of 15days;
18. What is the use of crosscheck command in RMAN?
Crosscheck will be useful to check whether the catalog information is intact with OS level information.
19. What are the differences between crosscheck and validate commands?
Crosscheck will verfies the backup files are available or expired
where as Validate will verifies the corrupted blocks in the backupsets
20. Which is one is good, differential (incremental) backup or cumulative (incremental) backup?
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0
21. What is Level 0, Level 1 backup?
A level 0 incremental backup, which is the base for subsequent incremental backups, copies all blocks containing data, backing the datafile up into a backup set just as a full backup would. A level 1 incremental backup can be either of the following types:
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0
22. Can we perform level 1 backup without level 0 backup?
If no level 0 backup is available, then the behavior depends upon the compatibility mode setting. If compatibility < 10.0.0, RMAN generates a level 0 backup of the file contents at the time of the backup. If compatibility is >= 10.0.0, RMAN copies all blocks changed since the file was created, and stores the results as a level 1 backup. In other words, the SCN at the time the incremental backup is taken is the file creation SCN.
23. Will RMAN put the database/tablespace/datafile in backup mode?
Nope.
24. What is snapshot control file?
As RMAN needs a consistent view of the control file it takes a backup of the controlfile by creating a snapshot and during the backup RMAN uses the snapshot of the controlfile. By default the snapshot controlfile is created in $ORACLE_HOME/dbs/snapcf_ORACLE_SID.f which can be changed by setting the following parameter in RMAN
25. What is the difference between backup set and backup piece?
Backup set is logical and backup piece is physical.
26. RMAN command to backup for creating standby database?
RMAN> duplicate target database to standby database ....
27. How to do cloning by using RMAN?
RMAN> duplicate target database …
28. You loss one datafile and DB is running in ARCHIVELOG mode. You have full database backup of 1 week/day old and don’t have backup of this (newly created) datafile. How do you restore/recover file?
create the datafile and recover that datafile.
SQL> alter database create datafile ‘…path..’ size n;
RMAN> recover datafile file_id;
29. 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.
30. What is the difference between hot backup & RMAN backup?
For hot backup, we have to put database in begin backup mode, then take backup.
RMAN won’t put database in backup mode.
31. How to put manual/user-managed backup in RMAN (recovery catalog)?
By using catalog command.
RMAN> CATALOG START WITH '/tmp/backup.ctl';
32. What are new features in Oracle 11g RMAN?
33. What is the difference between auxiliary channel and maintenance channel?
Recovery Manager (RMAN) is a utility that can manage your entire Oracle backup and recovery activities.
Which Files must be backed up?
Database Files (with RMAN)
Control Files (with RMAN)
Offline Redolog Files (with RMAN)
INIT.ORA (manually)
Password Files (manually)
2. When you take a hot backup putting Tablespace in begin backup mode, Oracle records SCN # from header of a database file. What happens when you issue hot backup database in RMAN at block level backup? How does RMAN mark the record that the block has been backed up ? How does RMAN know what blocks were backed up so that it doesn't have to scan them again?
In 11g, there is Oracle Block Change Tracking feature. Once enabled; this new 10g feature records the modified since last backup and stores the log of it in a block change tracking file. During backups RMAN uses the log file to identify the specific blocks that must be backed up. This improves RMAN's performance as it does not have to scan whole datafiles to detect changed blocks.
Logging of changed blocks is performed by the CTRW process which is also responsible for writing data to the block change tracking file. RMAN uses SCNs on the block level and the archived redo logs to resolve any inconsistencies in the datafiles from a hot backup. What RMAN does not require is to put the tablespace in BACKUP mode, thus freezing the SCN in the header. Rather, RMAN keeps this information in either your control files or in the RMAN repository (i.e., Recovery Catalog).
3. What are the Architectural components of RMAN?
1.RMAN executable
2.Server processes
3.Channels
4.Target database
5.Recovery catalog database (optional)
6.Media management layer (optional)
7.Backups, backup sets, and backup pieces
4. What are Channels?
A channel is an RMAN server process started when there is a need to communicate with an I/O device, such as a disk or a tape. A channel is what reads and writes RMAN backup files. It is through the allocation of channels that you govern I/O characteristics such as:
Type of I/O device being read or written to, either a disk or an sbt_tape
Number of processes simultaneously accessing an I/O device
Maximum size of files created on I/O devices
Maximum rate at which database files are read
Maximum number of files open at a time
5. Why is the catalog optional?
Because RMAN manages backup and recovery operations, it requires a place to store necessary information about the database. RMAN always stores this information in the target database control file. You can also store RMAN metadata in a recovery catalog schema contained in a separate database. The recovery catalog
schema must be stored in a database other than the target database.
6. What does complete RMAN backup consist of ?
A backup of all or part of your database. This results from issuing an RMAN backup command. A backup consists of one or more backup sets.
7. What is a Backup set?
A logical grouping of backup files -- the backup pieces -- that are created when you issue an RMAN backup command. A backup set is RMAN's name for a collection of files associated with a backup. A backup set is composed of one or more backup pieces.
8. What is a Backup piece?
A physical binary file created by RMAN during a backup. Backup pieces are written to your backup medium, whether to disk or tape. They contain blocks from the target database's datafiles, archived redo log files, and control files. When RMAN constructs a backup piece from datafiles, there are a several rules that it follows:
A datafile cannot span backup sets
A datafile can span backup pieces as long as it stays within one backup set
Datafiles and control files can coexist in the same backup sets
Archived redo log files are never in the same backup set as datafiles or control files RMAN is the only tool that can operate on backup pieces. If you need to restore a file from an RMAN backup, you must use RMAN to do it. There's no way for you to manually reconstruct database files from the backup pieces. You must use RMAN to restore files from a backup piece.
9. What are the benefits of using RMAN?
1. Incremental backups that only copy data blocks that have changed since the last backup.
2. Tablespaces are not put in backup mode, thus there is noextra redo log generation during online backups.
3. Detection of corrupt blocks during backups.
4. Parallelization of I/O operations.
5. Automatic logging of all backup and recovery operations.
6. Built-in reporting and listing commands.
10. Difference between catalog and nocatalog?
Ans : the difference is only who maintains the backup records like
when is the last successful backup incremental differential etc.
In CATALOG mode another database (TARGET database) stores all the information.
In NOCATALOG mode controlfile of Target database is responsible.
12. Difference between using recovery catalog and control file?
When new incarnation happens, the old backup information in control file will be lost. It will be preserved in recovery catalog.
In recovery catalog, we can store scripts.
Recovery catalog is central and can have information of many databases.
13. Can we use same target database as catalog?
No. The recovery catalog should not reside in the target database (database to be backed up), because the database can't be recovered in the mounted state.
14. How do u know how much RMAN task has been completed?
By querying v$rman_status or v$session_longops
15. From where list & report commands will get input?
16. Command to delete archive logs older than 7days?
RMAN> delete archivelog all completed before sysdate-7;
17. How many days backup, by default RMAN stores?
We have to specify the retention policy for that...using
RMAN>configure rentention policy for the recovery window of 15days;
18. What is the use of crosscheck command in RMAN?
Crosscheck will be useful to check whether the catalog information is intact with OS level information.
19. What are the differences between crosscheck and validate commands?
Crosscheck will verfies the backup files are available or expired
where as Validate will verifies the corrupted blocks in the backupsets
20. Which is one is good, differential (incremental) backup or cumulative (incremental) backup?
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0
21. What is Level 0, Level 1 backup?
A level 0 incremental backup, which is the base for subsequent incremental backups, copies all blocks containing data, backing the datafile up into a backup set just as a full backup would. A level 1 incremental backup can be either of the following types:
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0
22. Can we perform level 1 backup without level 0 backup?
If no level 0 backup is available, then the behavior depends upon the compatibility mode setting. If compatibility < 10.0.0, RMAN generates a level 0 backup of the file contents at the time of the backup. If compatibility is >= 10.0.0, RMAN copies all blocks changed since the file was created, and stores the results as a level 1 backup. In other words, the SCN at the time the incremental backup is taken is the file creation SCN.
23. Will RMAN put the database/tablespace/datafile in backup mode?
Nope.
24. What is snapshot control file?
As RMAN needs a consistent view of the control file it takes a backup of the controlfile by creating a snapshot and during the backup RMAN uses the snapshot of the controlfile. By default the snapshot controlfile is created in $ORACLE_HOME/dbs/snapcf_ORACLE_SID.f which can be changed by setting the following parameter in RMAN
25. What is the difference between backup set and backup piece?
Backup set is logical and backup piece is physical.
26. RMAN command to backup for creating standby database?
RMAN> duplicate target database to standby database ....
27. How to do cloning by using RMAN?
RMAN> duplicate target database …
28. You loss one datafile and DB is running in ARCHIVELOG mode. You have full database backup of 1 week/day old and don’t have backup of this (newly created) datafile. How do you restore/recover file?
create the datafile and recover that datafile.
SQL> alter database create datafile ‘…path..’ size n;
RMAN> recover datafile file_id;
29. 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.
30. What is the difference between hot backup & RMAN backup?
For hot backup, we have to put database in begin backup mode, then take backup.
RMAN won’t put database in backup mode.
31. How to put manual/user-managed backup in RMAN (recovery catalog)?
By using catalog command.
RMAN> CATALOG START WITH '/tmp/backup.ctl';
32. What are new features in Oracle 11g RMAN?
33. What is the difference between auxiliary channel and maintenance channel?
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