Immediately after backing up the database, verify that the backup does not contain any corrupted blocks. Use the Restore (PROREST) utility to verify the integrity of a full or incremental backup of a database as follows:
Run PROREST with the Partial Verify (-vp) parameter. With this parameter, PROREST checks the backup for bad blocks and reports whether any exist.
Run PROREST with the Full Verify (-vf) parameter. With this parameter, PROREST compares the backup to the database block-for-block.
These parameters do not actually restore the database. They only verify the status of the backup, notify you if there are any bad blocks, and report whether the blocks are recoverable. You must run the restore utility again (without the partial or full verify parameters) to restore the database.
When you use the -vp parameter, PROREST scans the backup and recalculates the CRC code for each block. It then compares the newly calculated CRC code with the CRC code stored in the block header. If the codes do not match, PROREST marks the block as bad and displays the following message:
CRC check failed reading backup block n
If the backup contains error-correction blocks and a redundancy set contains only one bad block, PROREST uses the error-correction block (and the other blocks in the redundancy set) to re-create the bad block. The error-correction block is the EXCLUSIVE OR of the backup blocks in the redundancy set. When PROREST recovers the block, the following message appears:
Recovered backup block n
If the redundancy set contains more than one bad block or if the backup does not include error-correction blocks, PROREST cannot recover the bad block and displays the following message:
n CRC error within recovery group - recovery impossible
PROREST also cannot recover a corrupted block if the error-correction block itself has a CRC check failure. In this case, the following message appears:
Unable to recover previous block in error
If PROREST encounters 10 unrecoverable errors during the verify pass or during the database restore, you can terminate the verify operation, as shown:
10 read errors have occurred.
Do you want to continue? [y/n]
Run PROREST with the Partial Verify (-vp) parameter. With this parameter, PROREST checks the backup for bad blocks and reports whether any exist.