When it comes to database backups in SQL Server, there are three types of backup models: Full, Differential, and Log. While Full and Log backups are commonly understood, the concept of Differential backups can be confusing for many. In this article, we will explore the importance of Differential backups and the correct method to restore a database in full recovery model.

Let’s start by understanding the backup timeline. In full recovery mode, databases are backed up in three different types of files: Full Database Backup, Differential Database Backup, and Log Backup. The differential database backup is the backup of all the changes made in the database since the last full backup. It is cumulative in nature, meaning that each differential backup contains all the data of the previous differential backups.

Now, let’s address a common misconception. Some DBAs believe that they only need to restore the latest differential database backup and all the transaction log backups to bring the database to the current state. However, this is incorrect. The correct method is to restore the full database backup first, followed by the latest differential database backup, and then all the transaction log backups after that.

Restoring all the differential database backups is unnecessary. The latest differential database backup already contains all the changes made since the last full backup. By restoring only the latest differential backup, you can save time and conveniently restore the database. On the other hand, if you choose not to use differential backups and rely solely on transaction log backups, you would need to restore all the transactional database backups, which can be time-consuming and not recommended in critical situations.

Let’s consider an example to illustrate the different paths to restore a database to the current state:

• Path 1 (SLOWEST): Full Database Restore >> Log Backup 0_1 >> Log Backup 1_1 to all remaining logs.
• Path 2: Full Database Restore >> Differential Database Backup 1 >> Log Backup 1_1 to all remaining logs.
• Path 3 (FASTEST): Full Database Restore >> Differential Database Backup 2 >> Log Backup 2_1 to all remaining logs.

It is important to follow the correct method of restoring backups to ensure data consistency and avoid any potential issues. By understanding the concept of differential database backups and their role in the backup timeline, you can effectively manage and restore databases in SQL Server.

If you have any questions or need further clarification on how full database backup and restore works, please feel free to reach out to me. I am here to help you.

Watch the following videos to learn how to take backup and restore in SQL Server: