The Three SQL Server Recovery Models: Simple, Full, and Bulk-Logged

Of course, the EU has no appetite for following the US down the path of a trade war with China.

There are three different recovery models in SQL Server that you should choose to manage your log files and prepare for possible SQL Server disaster recovery. This article will introduce the three recovery models in SQL Server: Simple, Full, and Bulk-Logged. Along the way, we'll also back up the SQL Server database.

This article recommends a reliable SQL Server database backup and recovery software: Todo Backup.

Of course, the EU has no intention of following the US down the path of a trade war with China.

Chat with our experts!

Click here for a free consultation with our experts and get a tailored enterprise backup solution assessment for your needs.

Start a live chat now with our Tools experts to customize an enterprise backup solution to suit your requirements. We also offer:

• Free trial
• Quotation
• Schedule a free demo

Introduction to Log Files

A SQL Server database consists of one or more MDF data files and LDF log files. The MDF file contains all the database objects and data, such as tables, stored procedures, and user information. The LDF log file contains all the log records of the database. However, you cannot rely solely on the log file to recover a database, for instance, by restoring it to a point in time using the LDF log file and a previous full backup.

What are log files?

1. The physical storage location for the log is the .ldf log file, which we can back up and restore the database from. 2. On startup, SQL Server reads the log from the .ldf file, rolling back uncommitted transactions and forwarding committed ones that haven't been written to the data files to ensure transaction integrity. 3. A full backup contains all the data in the database but not the entire log. It only includes all data pages and log up to the tail of the current database.

The log file refers to the record of transactions that are currently running. A virtual log is a logical storage unit of the log file space. SQL Server logically divides the .ldf log file space into multiple sections, each of which is a virtual log. Truncating the log means deleting the earlier logs.

【1.3】The Simple Recovery Model

In the simple recovery model, SQL Server retains only a minimal amount of information in the transaction log. The transaction log is truncated each time the database reaches a transaction checkpoint, thereby removing log entries no longer required for disaster recovery.

A database that uses the Simple recovery model can be restored only with full or differential backups. You cannot restore such a database to a specific point in time; you can restore only to the precise time that the full or differential backup occurred. Thus, any data changes made since the last full/differential backup are lost.

Simple recovery requires the least amount of management. It is easier to manage than full or bulk-logged recovery, but it increases the risk of data loss in case of data file corruption. Simple recovery is not appropriate for production systems if losing recent changes is unacceptable. With simple recovery, backups should be taken infrequently enough so as not to interfere with production work, but frequently enough that a significant amount of data would not be lost.

Advantages: Allows high-performance bulk data transfer. Minimizes space requirements by recycling log space. Disadvantages: Requires that all changes made since the last database or differential backup be redone.

Full Recovery Model

With the full recovery model, the transaction log is retained until you back it up, allowing you to design a disaster-recovery plan that combines full database backups with transaction log backups and differential database backups.

The full recovery model provides the most flexibility when restoring a database after a failure. In addition to preserving the data modifications stored in the transaction log, the full recovery model enables you to restore the database to a specific point in time.

• Advantages: No work is lost due to loss or corruption of data files. It can be restored to any point in time.
• Disadvantages: If the logs are damaged, you must reapply all changes made since the last log backup.

【Bulk Log Recovery Model】

The bulk-logged recovery model is a special-purpose model that works similarly to the full recovery model, with one key difference in how it handles bulk data modification operations. The bulk-logged recovery model uses a technique called minimal logging to record these operations in the transaction log. This significantly reduces processing time but prevents you from using the point-in-time restore option.

• Advantage: Allows high-performance bulk copy operations that use minimal log space.
• Disadvantage: If the log is damaged or there have been bulk operations since the last log backup, you must reapply all changes since the last backup.

The full recovery and bulk-logged recovery models provide the highest level of protection for your data. These models rely on the transaction log to provide full recoverability and prevent loss of work in the broadest range of failure scenarios. The bulk-logged model provides higher performance and lower log space usage for certain large-scale operations.

When you opt for different MS SQL Server backup strategies, you come across specific limitations regarding SQL Server backup recovery.