SQL Server LogShipping

SQL Server log shipping (Ship the T-logs) is a technique which involves two or more SQL Server instances and copying of a transaction log file from one SQL Server instance to another. The process of transferring the transaction log files and restoring is automated across the SQL Servers. As the process result there are two copies of the data on two separate locations.

A log shipping session involves the following steps:

• Backing up the transaction log file on the primary SQL Server instance
• Copying the transaction log backup file across the network to one or more secondary SQL Server instances
• Restoring the transaction log backup file on the secondary SQL Server instances

Implementation examples

One of the common log shipping scenarios is the environment with two servers (SQLServer-1 – primary and SQLServer-2 – secondary), two SQL Server instances (SQLInstance-1 and SQLInstance-2), and one SQL Server database named SQLDB-1 with log shipping running on it.



Common SQL Server log shipping scenarios - the environment with two servers

Another common configuration is the environment with three (or more) servers (SQLServer-1 – primary, SQLServer-2 – secondary, and SQLServer-3 – secondary), three SQL Server instances (SQLInstance-1, SQLInstance-2, and SQLInstance-3), and one SQL Server database named SQLDB-1 with log shipping running on it
 


SQL Server Log shipping scenarios - The environment with three (or more) servers
Operating modes

There are two available modes and they are related to the state in which the secondary, log shipped, SQL Server database will be:

•     Standby mode – the database is available for querying and users can access it, but in read-only mode
• The database is not available only while the restore process is running
• Users can be forced to disconnect when the restore job commence
• The restore job can be delayed until all users disconnect themselves
•     Restore mode – the database is not accessible

Advantages and disadvantages of using SQL Server log shipping

SQL Server log shipping is primarily used as a disaster recovery solution. Using SQL Server log shipping has multiple benefits: it’s reliable and tested in details, it’s relatively easy to set up and maintain, there is a possibility for failover between SQL Servers, data can be copied on more than one location etc.

Log shipping can be combined with other disaster recovery options such as AlwaysOn Availability Groups, database mirroring, and database replication. Also, SQL Server log shipping has low cost in human and server resources

The main disadvantages in the SQL Server log shipping technique are: need to manage all the databases separately, there isn’t possibility for an automatic failover, and secondary database isn’t fully readable while the restore process is running.

Requirements

• You need three SQL Servers or at least three SQL Server Instances (three instances can be used for testing purposes only, but it is not recommended for production environments). In this sample we will use 2 Servers.
• You can use SQL Server Enterprise, Standard, Business Intelligence or Web Edition for this article.
• Create a folder and assign permissions to the SQL Server Agent Account to this folder on the principal server. In this example, the folder name will be logshipping in the c:\ drive.
• Create a folder and assign permissions to the SQL Server Agent Account to this folder on the secondary server. In this example, the folder name will be destination in the c:\ drive.