SQL Server Disaster Recovery Plan

For SQL database administrators, ensuring database availability 24X7 is crucial for continuous business operations. However, incidents like natural disasters, malware attack, etc. can cause database downtime and data loss. Therefore, organizations need to have a Disaster Recovery (DR) plan in place to quickly restore the database to avoid downtime and ensure safe data recovery.

A DR plan provides a structured approach to respond to any unplanned incident. It tells you from where to start and the solutions to consider for preventing data loss.

Before We Proceed

It is important to understand the difference between High Availability (HA) and Disaster Recovery (DR). You’ll hear about HA (High Availability) and DR (Disaster Recovery) together as the business continuity solutions – aimed at keeping SQL Server databases in an operational state. While both HA and DR have similar goals of keeping databases up and running in a functional state, they are distinctively separate technologies.?

What is High Availability and Disaster Recovery in SQL Server?

High Availability (HA) in SQL Server is about ensuring that the server and databases are always available with minimal downtime. Essentially, a High Availability plan is to ensure decreased recovery time objective (RTO). However, the less is downtime, the more expensive the solution is.

Disaster Recovery (DR) in SQL Server is about how much data loss (i.e., RPO or recovery point objective) is tolerable. For instance, losing one minute of data can be a disaster for a bank – compared to the organization that needs data for generating monthly sales reports. And so, all the DR plans are not the same. A DR plan needs to be tailored to meet your data protection needs when a disruptive event occurs.

Besides understanding the difference between HA and DR, you must also take into account RTO and RPO: Useful Considerations for SQL Server Disaster Recovery to create a disaster recovery plan. Understanding the RTO and RPO requirements is crucial when developing a DR plan because you need to balance the risk of losing data against the cost of implementing a disaster recovery solution.

Disaster Recovery Options in SQL Server

There are several DR options built into SQL Server for minimizing the impact of disaster situations. Here, we will be discussing the three most significant disaster recovery techniques.

• Backup and Restore

After a failure, the first step to restoring databases starts with backup and restore. The backup and restore option is available in every edition of SQL Server and can return databases to a consistent state without the risk of data loss. For creating backups, you need full backups, differential backups, and log backups. However, you may or may not take differential backups in case you're experiencing disk issues or have time constraints. You can write scripts or use PowerShell to back up a SQL database.

Once you have backed up, it is essential to frequently perform test restores on the backup to ensure it is not corrupted. You can do so by restoring the database on a test server.

Pros

• Implementing a backup and restore DR solution is simple and inexpensive.
• Allows saving multiple copies of the database in different locations.

Cons

• The backup and restore technique can only be used on databases set to the Full recovery model.
• Log Shipping

Log Shipping is another disaster recovery option that uses the backup and restore capabilities of SQL Server to create a database replica for failover. More specifically, log shipping allows the database backup and its subsequent transaction logs to be backed up from the primary server, and the backups are shipped to one or more secondary databases on the secondary server and restored (applied) there. Once log shipping is configured, you can create Agent jobs to get alerts on scheduled backup failure, copy, and restore operations.

Though log shipping is easy to configure, you need to manually switch the primary database to a secondary database, which can be time-consuming.

Pros

• Easier to set up and manage.
• Log shipping allows having more than one secondary server. This is great as you can have one dedicated server for DR and another for off-loading reads for reporting instances.

Cons

• Does not support automatic failover.
• Jobs or logins that are not stored at the database level but stored at the system database level need to be created manually.?
• AlwaysOn Availability Groups

You can use the AlwaysOn Availability Groups as a DR and HA solution. It's just like database mirroring (a deprecated DR technique that is still available for use). The AlwaysOn Availability Groups provide multiple mirrors of databases that you can fail over in groups to a secondary server. SQL Server can support up to eight secondary databases in an availability group.

Pros

• Ability to failover multiple databases.
• Automatic fault tolerance.
• Ensures zero data loss protection.
• Allows off-loading read operations to any readable secondary database from the primary replica.

Cons

• It is expensive and complex to set up.
• Logins are difficult to manage.

Conclusion

In a disaster scenario, one of the biggest concerns of every SQL DBA is performing disaster recovery (DR) while ensuring that the data is intact. Having a DR plan is critical for maintaining business continuity. This article discussed some important considerations for a disaster recovery plan.

On the other hand, your SQL Server databases can turn corrupt or inaccessible due to sudden power outage, hardware failure, or software bug. Having the right tools at your disposal can help you quickly recover the data without much efforts. Using a specialized SQL recovery tool like Stellar Repair for MS SQL can help fix any corruption errors in the database files (MDF and NDF) and recover its data.