Backup Verify

Use

When making database backups, you must regularly perform a verify.

If you fail to verify backups, you might find that a backup cannot be used in the event of a database restore. Even if a backup is reported as successfully completed, this does not mean that it is always error-free.

There are the following types of verify:

• Backup tape readability

This verify checks the backup media (that is, usually tape). It checks the size of the backup files and whether the data can be read. In some cases, it also compares the backed-up data with the contents of the database byte-by-byte.

• Database block consistency

This verify checks the database itself block-by-block.

At least once in every backup cycle, you must perform both types of verify. If possible, perform verify once a week, or even for every backup.

Integration

• You can perform verify at the command level of the
BRBACKUP, BRARCHIVE, and BRRESTORE tools, as described below.
• You can also perform verify using the
action patterns of the DBA Planning Calendar.

Prerequisites

• Verify adds considerably to backup run times.
• Verify is always performed on complete backup volumes. A volume is first written and then verified.

Features

Verify of Backups with BRBACKUP

This type of verify only checks the backup tape readability. The method and extent of a BRBACKUP verify differs according to whether the backup is online or offline:

• Offline backup

After the backup the files are copied back to a temporary directory, compress_dir, and the contents are compared to the original data in the database byte by byte.

• Online backup

After the backup the files are copied back to a temporary directory, compress_dir, but only the readability file sizes are compared. The byte-by-byte compare used in an offline backup is not possible with an online backup because the database is constantly changing as updates continue.

Independent Verify of Backups with BRRESTORE

This type of verify with BRRESTORE only checks the backup tape readability, separately from the backup, at a later time if you want. You can also perform this type of verify on another computer.

BRRESTORE only checks whether the backup can be read and its size, not the contents. The files are only read, not restored.

Verify of Backups with BRARCHIVE

This type of verify with BRARCHIVE only checks the backup tape readability. The extent of the check on archived offline redo log files depends on the type of BRARCHIVE backup:

• brarchive -s|-sc|-ss|-cs

The backed-up files are restored and compared with the originals byte by byte.

• brarchive -sd|-scd|-ssd|-cds

The file sizes of the archived offline redo log files are checked. Since the originals were deleted, a check on the contents is not possible.

Verify of Backups with Oracle DBVERIFY

The Oracle DBVERIFY tool is available for both types of verify, that is, backup tape readability (but without a byte-by-byte comparison) and database block consistency. This means you can recognize errors early (for example, ORA-1578), before they lead to the termination of a program in an application that accesses the blocks.

You can use DBVERIFY as follows:

• Database backup with subsequent restore to a temporary directory (
compress_dir) and check on the Oracle block structure:

brbackup -w use_dbv

• Online check of block structure on the database files without backup:

brbackup -w only_dbv

Any number of these verify processes can run in parallel, using parameter exec_parallel, option -e.

• Temporary restore of a database backup (
compress_dir) and verify of the database block consistency:

brrestore -w use_dbv

The restore implicitly checks the readability of the backup.

Verify of BACKINT Backups

You can verify third-party backups using the BACKINT interface. This function confirms that backups are known to the external backup tool (that is, confirmation) and they are accepted when restoring. In this case there is no physical data check on the backup medium. Only an internal catalog of BACKINT backups of the backup tool is checked (that is, logical verification). Verifications using Oracle DBVERIFY are no longer supported in this context.

If you want to include verification of the internal Oracle block
consistency with DBVERIFY, you can check the database directly without
starting the backup. To do this, call BRBACKUP as follows:

brbackup -w only_dbv

From Release 4.5A, the external backup tool – that is, backup_dev_type = rman_util – can also be accessed using the Oracle Recovery Manager (RMAN). This gives you a complete range of functions for verification:

• The RMAN validate function is used for verifying backups. In this case, data is physically read by the backup medium and checked by RMAN for consistency.
• The verification with DBVERIFY is no longer required because for each backup all saved database files are checked by RMAN for internal Oracle block consistency.

You can also use BR programs from Release 4.5 for RMAN backups for lower SAP releases. Oracle 8.0 is required in this case. For more information, see Note 12741.

Of course, you can perform BACKINT backup verification directly using the backup tool (if supported). Some backup tools offer special parameters in the BACKINT parameter file, init.utl, that you can use to activate the verification independent of the BR option -w|-verify. For additional information, consult your BACKINT provider.