The next level is crash-consistent backup. This method doesn’t save any data from system memory and might have an issue with access to files locked for reading. Further, many files that make up the guest operating system of the VM may have different timestamps making an unclear recovery point. In this case, backup will not be equal to original system files. If a change in the files happens while backup is running, then the result is an inconsistent backup. It can be easily imagined as a simple file copy operation which brings all computer files to another place such as a disk drive, USB disk or a NAS. The first and oldest is inconsistent backup. Let’s consider these levels of backup consistency one by one. There are a few levels of backup consistency which can be identified by whether backup can be taken from the live system, if interdependent files are assured to be identical and whether there is protection against transactional data loss (application-aware). It always matters, especially when the data is being changed actively like in bank systems, simultaneously making thousands of financial transactions within an account database. Today, it’s hard to imagine a situation when data consistency doesn’t matter for a company.

In this blog, I will discuss data consistency in more detail, define different levels of consistent backups and explain how to make sure that your Veeam backup is consistent. This is a critical characteristic of any backup solution.

Data consistency is the sum of validity, accuracy, usability and integrity of data between applications and across an operating system.

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