There can be situations when the data on the tape media could be physically corrupted. In such cases, IBM Spectrum Protect can help validate the data is not damaged by using the command explained below. But, what if the data is instead logically inconsistent? In this blog post, you can find the configuration best practice to follow to check for both.
Physically corrupted means that there is something wrong and the data cannot be accessed nor read at all by the backup application. Even though IBM Spectrum Protect is able to read the data, it doesn’t necessarily mean that the data is usable. There are cases when the application cannot make sense of the data to use it again when needed; therefore, the data is logically inconsistent.
To verify the data is not logically inconsistent, IBM Spectrum Protect offers the Audit Volume command. There are best practices you need to keep in mind and perform when you schedule the Audit Volume command.
The Audit Volume Command is used to check if the data can be accessed and is physically readable. The Audit Volume command also checks for inconsistencies between database information and a storage pool volume.
The Audit Volume Command is: audit volume fix= parameter yes/no
To check for data integrity, the Audit Volume validates the backup and archived data at the object level and verifies objects against the database. It’s able to indicate which object is available on a particular volume or is missing.
However, it’s important that when scheduling an Audit Volume command, the CRCDATA parameter is also enabled for each storage pool before data is backed up. The default for CRCDATA is NO. This setting has to be enabled, otherwise, it will not validate the integrity of the data nor detect logical inconsistencies because it will not have the information to compare the file against the original in the database.
What is the CRCData command? According to the IBM Knowledge center (link here https://www.ibm.com/support/knowledgecenter/SSEQVQ_8.1.4/srv.reference/r_cmd_stgpool_activedata_seq_update.html) the CRCData command:
“Specifies whether a cyclic redundancy check (CRC) validates storage pool data when audit volume processing occurs on the server. This parameter is only valid for NATIVE data format storage pools. This parameter is optional. The default value is NO. By setting CRCDATA to YES and scheduling an AUDIT VOLUME command, you can continually ensure the integrity of data that is stored in your storage hierarchy. You can specify the following values:
Yes: Specifies that data is stored containing CRC information, allowing for audit volume processing to validate storage pool data. This mode impacts performance because more processing is required to calculate and compare CRC values between the storage pool and the server.
No: Specifies that data is stored without CRC information.”
Detecting physically corrupted and logically inconsistent data can be a challenge when working with a large amount of tape media. Tape Audit Tool is one solution that provides automation for the audit process and by default ensures the data is both available and logically readable. This solution is a user interface that acts as a front-end to Spectrum Protect and provides automation, control and efficiency when setting up the audit process. Check Tape Audit Tool for more information. (https://www.svasoftware.com/backup-archive/tape-audit-tool/)
Backups that were executed without CRCDATA enabled, would not make use of the AUDIT for data integrity. This is the reason why it’s good practice to turn the CRCDATA today on backups so that the audit could validate the CRCDATA on those in the future.