Verify Jobs Functions

In Bacula, Verify Jobs perform three important tasks to ensure data integrity:

Verify Volume Data Integrity
Verify Volume Metadata Integrity
Verify File System Integrity

While the goals are quite different, the setup for all types of Verify Jobs share a good deal of the configuration (which is due to the fact that they also share a good deal of program code). However, it is important to understand the differences between these types of verification.

Once data is backed up, it is important to ensure that the backed up data is stored correctly. Today, modern tape drives do Read-after-Write to detect errors writing data and re-write that data automatically, but this approach can only find errors occuring between the drive and the tape media. Data corruption happening at earlier stages, for example while transferring data from the host computer to the storage device can not be found using this technology.

As there are many – and, often, very complex – layers of data processing between the application and the storage media, data can become corrupted long before it arrives at the storage device. 1 This sort of problems can only be detected by the software generating the data. To do this detection, the stored data needs to be read and compared to what is expected on the storage media.