SQL Server Log Shipping

Log shipping is a disaster recovery solution that allows you to automatically send transaction log backups from one or more primary databases to a set of secondary databases. This mechanism enables you to keep secondary databases in a warm standby or cold standby state, ready to be brought online if the primary database becomes unavailable.

It's a cost-effective and relatively simple method for ensuring data redundancy and a quick recovery point objective (RPO) without requiring complex infrastructure.

Key Benefits of Log Shipping

Disaster Recovery: Provides a robust solution to recover your databases in case of hardware failures, natural disasters, or other catastrophic events.
High Availability (Read-Only): Secondary databases can be configured to be in a RESTORING state with NORECOVERY, allowing for read-only access to historical data if needed (requires careful management).
Cost-Effective: Generally less complex and expensive to implement compared to other HA solutions like Always On Availability Groups.
Simplicity: The setup and management process is straightforward, making it accessible for many DBAs.
Data Protection: Minimizes data loss by regularly backing up and restoring transaction logs.

Implementing Log Shipping

Setting up log shipping involves several key components and steps:

1. Primary Database Configuration

Ensure your primary database is in the FULL recovery model and has regular transaction log backups scheduled.

2. Backup Share and Permissions

Create a network share where transaction log backups will be copied. Ensure the SQL Server service accounts have appropriate read/write permissions.

3. Copy Jobs

Configure a SQL Server Agent job on the primary server to copy the transaction log backups from the primary server's backup directory to the network share.

4. Restore Jobs

On each secondary server, configure SQL Server Agent jobs to restore the copied transaction log backups to the secondary databases.

5. Monitoring

Implement a robust monitoring strategy to ensure backups are taken, copied, and restored successfully. SQL Server Management Studio (SSMS) provides built-in log shipping monitoring tools.

Core Components:

Primary Database: The source database that generates transaction log backups.
Transaction Log Backups: The essential data files that are transferred.
Backup Share: A network location where backups are stored before being copied.
Copy Job: A SQL Server Agent job that moves log backups to the backup share.
Restore Job: SQL Server Agent jobs that apply the log backups to the secondary databases.
Secondary Databases: Standby copies of the primary database.

Example Configuration Steps (using SSMS):

Right-click the primary database, select Tasks > Ship Transaction Log.
In the Log Shipping dialog, click Add to configure a secondary.
Specify the Secondary server instance and Secondary database name.
Configure the Backup settings (backup share path, schedule).
Configure the Copy settings (destination folder on secondary, schedule).
Configure the Restore settings (restore in NORECOVERY or STANDBY mode, schedule).
Repeat for additional secondaries.
Enable log shipping.

Important Considerations

Recovery Model: The primary database MUST be in the FULL recovery model.
Network Latency: High network latency can delay backup copying and restoration, impacting RPO.
Disk Space: Ensure sufficient disk space on primary, backup share, and secondary servers.
Monitoring: Proactive monitoring is crucial. Investigate any failures immediately.
Full Backups: Log shipping relies on regular full and differential backups of the primary database. These need to be restored to the secondary database to establish a baseline before log shipping can begin.
Failover Process: Log shipping does not automate failover. You must manually take the secondary database online after a failure.
Transaction Log Size: Very large transaction logs can impact performance and transfer times.

While log shipping is excellent for disaster recovery, for higher availability scenarios with automatic failover, consider exploring Always On Availability Groups.