BLOCKRECOVER

Syntax

Text description of the illustration blockrecover.gif

bmrBlockSpec::=

Text description of the illustration bmrBlockSpec.gif

bmrOption::=

Text description of the illustration bmrOption.gif

Purpose

Block media recovery recovers an individual data block or set of data blocks within a datafile. This type of recovery is useful if the data loss or corruption applies to a small number of blocks rather than to an entire datafile.

You can also use block media recovery to validate the integrity of redo generated after a backup. For example, you can do a trial-run block media recovery to detect problems in the archived redo stream.

Typically, block corruption is reported in Oracle error messages in trace files. Block-level data loss usually results from:

• I/O errors causing minor data loss
• Memory corruptions that get flushed to disk

You need to specify the datafile number and block number or the tablespace and data block address (DBA) when executing the BLOCKRECOVER command, or use the CORRUPTION LIST keyword to recover all blocks reported in the V$DATABASE_BLOCK_CORRUPTION view.

Restrictions and Usage Notes

• This command is available only in the Enterprise Edition.
• The target database must be mounted or open. You do not have to take a datafile offline if you are performing block media recovery on it.
• You can only perform complete media recovery of individual blocks. Point-in-time recovery of individual data blocks is not supported.
• You can only perform block media recovery on corrupt blocks.
• Blocks marked media corrupt are not accessible until recovery completes.
• You cannot perform block media recovery when using a backup control file.
• You cannot use proxy backups to perform block media recovery. If the only backups that you have are proxy backups, then you can restore them to a nondefault location on disk, which causes RMAN to view the restored files as datafile copies. You can then use the datafile copies for block media recovery.
• You must have a full backup of the file containing the corrupt blocks: block media recovery cannot use incremental backups.
• Block media recovery cannot survive a missing or inaccessible archived log, although it can sometimes survive missing or inaccessible records (refer to Oracle9i Recovery Manager User's Guide).
• The datafile header block (block 1) cannot be recovered.
• You cannot perform block media recovery in NOARCHIVELOG mode.

Keywords and Parameters

Syntax Element	Description
DEVICE TYPE deviceSpecifier	Specifies the device type for the backup used in the block recovery. See Also: "deviceSpecifier"
bmrBlockSpec	Specifies the data blocks that require recovery.
DATAFILE datafileSpec	Specifies a list of one or more datafiles that contain blocks requiring recovery. See Also: "datafileSpec"
BLOCK integer	Specifies the block number of the block requiring media recovery. Typically, the block number is obtained from error message output.
TABLESPACE tablespace_name	Specifies the tablespace name or number containing the corrupt blocks.
DBA integer	Specifies the data block address (DBA) of the corrupt block.
CORRUPTION LIST	Recovers all blocks listed in the V$DATABASE_BLOCK_CORRUPTION view. This view displays blocks marked corrupt by the most recent BACKUP (with or without the VALIDATE option), VALIDATE, or COPY command. The following types of corruption result in rows added to this view: Physical corruption (sometimes called media corruption). Oracle does not recognize the block at all: the checksum is invalid, the block contains all zeros, or the header and footer of the block do not match. Physical corruption checking is on by default, and can be turned off with the NOCHECKSUM option. Logical corruption. The block has a valid checksum, the header and footer match, and so forth, but the contents are logically inconsistent. Logical corruption checking is off by default, and can be turned on with the CHECK LOGICAL option.
bmrOption	Specifies various restore options relating to the block recovery.
FROM BACKUPSET	indicates that only backup set should be restored.
FROM DATAFILECOPY	indicates that only datafile image copies should be restored.
FROM TAG = 'tag_name'	indicates that only the copy of the backup set with the specified tag should be restored. Tag names are not case sensitive. See Also: "BACKUP" to learn how a tag is applied to a copy of a backup set
RESTORE untilClause	Specifies that only backups and copies created before the specified time, SCN, or log sequence number should be restored. See Also: "untilClause"

Examples

Recovering a Group of Corrupt Blocks: Example

This example recovers corrupt blocks in three datafiles:

BLOCKRECOVER DATAFILE 2 BLOCK 12, 13 DATAFILE 3 BLOCK 5, 98, 99 DATAFILE 4 BLOCK 19;

Limiting Block Media Recovery by Type of Restore: Example

The following example recovers a series of blocks and restores only from datafile copies:

RUN
{
  BLOCKRECOVER DATAFILE 3 BLOCK 2,3,4,5 TABLESPACE sales DBA 4194405, 4194409, 4194412
  FROM DATAFILECOPY;
}

Limiting Block Media Recovery by Backup Tag: Example

This example recovers blocks and restores only from the backup set with the tag weekly_backup:

BLOCKRECOVER TABLESPACE SYSTEM DBA 4194404, 4194405 FROM TAG "weekly_backup";

Limiting Block Media Recovery by Time: Example

The following example recovers two blocks in the SYSTEM tablespace. It restores only from backups that could be used to recover the database to a point two days ago:

BLOCKRECOVER TABLESPACE SYSTEM DBA 4194404, 4194405 RESTORE UNTIL TIME 'SYSDATE-2';

Repairing All Block Corruption in the Database: Example

The following example runs a backup validation to populate V$DATABASE_BLOCK_CORRUPTION, then repairs any corrupt blocks recorded in the view:

BACKUP VALIDATE DATABASE;
BLOCKRECOVER CORRUPTION LIST;