16 Validating Database Files and Backups

Overview of RMAN Validation

This section explains the basic concepts and tasks involved in RMAN validation.

Checking for Block Corruption with the VALIDATE Command

You can use the VALIDATE command to manually check for physical and logical corruptions in database files. This command performs the same types of checks as BACKUP VALIDATE, but VALIDATE can check a larger selection of objects. For example, you can validate individual blocks with the VALIDATE DATAFILE ... BLOCK command.

When validating whole files, RMAN checks every block of the input files. If the backup validation discovers previously unmarked corrupt blocks, then RMAN updates the V$DATABASE_BLOCK_CORRUPTION view with rows describing the corruptions.

Use VALIDATE BACKUPSET when you suspect that one or more backup pieces in a backup set are missing or have been damaged. This command checks every block in a backup set to ensure that the backup can be restored. If RMAN finds block corruption, then it issues an error and terminates the validation. The command VALIDATE BACKUPSET enables you to choose which backups to check, whereas the VALIDATE option of the RESTORE command lets RMAN choose.

To use VALIDATE to check database files and backups:

1. Start RMAN and connect to a target database.

2. Execute the VALIDATE command with the desired options.

   For example, to validate all datafiles and control files (and the server parameter file if one is in use), execute the following command at the RMAN prompt:

   RMAN> VALIDATE DATABASE;
   

   Alternatively, you can validate a particular backup set by using the form of the command shown in the following example (sample output included).

   RMAN> VALIDATE BACKUPSET 22;
   
   Starting validate at 17-AUG-06
   using channel ORA_DISK_1
   allocated channel: ORA_SBT_TAPE_1
   channel ORA_SBT_TAPE_1: SID=89 device type=SBT_TAPE
   channel ORA_SBT_TAPE_1: Oracle Secure Backup
   channel ORA_DISK_1: starting validation of datafile backup set
   channel ORA_DISK_1: reading from backup piece /disk1/oracle/work/orcva/RDBMS/backupset/2007_08_16/o1_mf_nnndf_TAG20070816T153034_2g774bt2_.bkp
   channel ORA_DISK_1: piece handle=/disk1/oracle/work/orcva/RDBMS/backupset/2007_08_16/o1_mf_nnndf_TAG20070816T153034_2g774bt2_.bkp tag=TAG20070816T153034
   channel ORA_DISK_1: restored backup piece 1
   channel ORA_DISK_1: validation complete, elapsed time: 00:00:01
   Finished validate at 17-AUG-06
   

   The following example illustrates how you can check individual data blocks within a datafile for corruption.

   RMAN> VALIDATE DATAFILE 1 BLOCK 10;
    
   Starting validate at 17-AUG-06
   using channel ORA_DISK_1
   channel ORA_DISK_1: starting validation of datafile
   channel ORA_DISK_1: specifying datafile(s) for validation
   input datafile file number=00001 name=/disk1/oracle/dbs/tbs_01.f
   channel ORA_DISK_1: validation complete, elapsed time: 00:00:01
   List of Datafiles
   =================
   File Status Marked Corrupt Empty Blocks Blocks Examined High SCN
   ---- ------ -------------- ------------ --------------- ----------
   1    OK     0              2            127             481907
     File Name: /disk1/oracle/dbs/tbs_01.f
     Block Type Blocks Failing Blocks Processed
     ---------- -------------- ----------------
     Data       0              36
     Index      0              31
     Other      0              58
   
   Finished validate at 17-AUG-06
   

Make Parallel the Validation of a Datafile

If you need to validate a large datafile, then RMAN can make the work parallel by dividing the file into sections and processing each file section in parallel. If multiple channels are configured or allocated, and if you want the channels to make parallel the validation, then specify the SECTION SIZE parameter of the VALIDATE command.

If you specify a section size that is larger than the size of the file, then RMAN does not create file sections. If you specify a small section size that would produce more than 256 sections, then RMAN increases the section size to a value that results in exactly 256 sections.

To make parallel the validation of a datafile:

1. Start RMAN and connect to a target database. The target database must be mounted or open.

2. Run VALIDATE with the SECTION SIZE parameter.

   The following example allocates two channels and validates a large datafile. The section size is 1200 MB.

   RUN
   {
     ALLOCATE CHANNEL c1 DEVICE TYPE DISK;
     ALLOCATE CHANNEL c2 DEVICE TYPE DISK;
     VALIDATE DATAFILE 1 SECTION SIZE 1200M;
   }
   

Validating Database Files with BACKUP VALIDATE

You can use the BACKUP VALIDATE command to do the following:

• Check datafiles for physical and logical block corruption

• Confirm that all database files exist and are in the correct locations

When you run BACKUP VALIDATE, RMAN reads the files to be backed up in their entirety, as it would during a real backup. RMAN does not, however, actually produce any backup sets or image copies.

You cannot use the BACKUPSET, MAXCORRUPT, or PROXY parameters with BACKUP VALIDATE. To validate specific backup sets, run the VALIDATE command.

To validate files with the BACKUP VALIDATE command:

1. Start RMAN and connect to a target database and recovery catalog (if used).

2. Run the BACKUP VALIDATE command.

   For example, you can validate that all database files and archived logs can be backed up by running a command as shown in the following example. This command checks for physical corruptions only.

   BACKUP VALIDATE 
     DATABASE 
     ARCHIVELOG ALL;
   

   To check for logical corruptions in addition to physical corruptions, run the following variation of the preceding command:

   BACKUP VALIDATE 
     CHECK LOGICAL 
     DATABASE 
     ARCHIVELOG ALL;
   

   In the preceding examples, the RMAN client displays the same output that it would if it were really backing up the files. If RMAN cannot back up one or more of the files, then it issues an error message. For example, RMAN may show output similar to the following:

   RMAN-00571: ===========================================================
   RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
   RMAN-00571: ===========================================================
   RMAN-03002: failure of backup command at 08/29/2007 14:33:47
   ORA-19625: error identifying file /oracle/oradata/trgt/arch/archive1_6.dbf
   ORA-27037: unable to obtain file status
   SVR4 Error: 2: No such file or directory
   Additional information: 3
   

Validating Backups Before Restoring Them

You can run RESTORE ... VALIDATE to test whether RMAN can restore a specific file or set of files from a backup. RMAN chooses which backups to use.

The database must be mounted or open for this command. You do not have to take datafiles offline when validating the restore of datafiles, because validation of backups of the datafiles only reads the backups and does not affect the production datafiles.

When validating files on disk or tape, RMAN reads all blocks in the backup piece or image copy. RMAN also validates offsite backups. The validation is identical to a real restore operation except that RMAN does not write output files.

To validate backups with the RESTORE command:

1. Run the RESTORE command with the VALIDATE option.

   This following example illustrates validating the restore of the database and all archived redo logs:

   RESTORE DATABASE VALIDATE;
   RESTORE ARCHIVELOG ALL VALIDATE;
   

   If you do not see an RMAN error stack, then skip the subsequent steps. The lack of error messages means that RMAN had confirmed that it can use these backups successfully during a real restore and recovery.

2. If you see error messages in the output and the RMAN-06026 message, then investigate the cause of the problem. If possible, correct the problem that is preventing RMAN from validating the backups and retry the validation.

   The following error means that RMAN cannot restore one or more of the specified files from your available backups:

   RMAN-06026: some targets not found - aborting restore
   

   The following sample output shows that RMAN encountered a problem reading the specified backup:

   RMAN-03009: failure of restore command on c1 channel at 12-DEC-06 23:22:30
   ORA-19505: failed to identify file "oracle/dbs/1fafv9gl_1_1"
   ORA-27037: unable to obtain file status
   SVR4 Error: 2: No such file or directory
   Additional information: 3