The Ultimate Manual To SQL Server Disaster Recovery

At any given time, your organization will have data relating to customers, employees, suppliers, and other stakeholders. It’s your responsibility to keep this safe from unauthorized eyes while keeping it easily accessible to ensure smooth operations.

While this would have been challenging a few years ago, it isn’t anymore.

The Microsoft SQL server has completely transformed the way businesses handle data. It’s built on top of SQL, a standard programming language for interacting with relational databases, and works exclusively on the Windows and Linux environments. This allows for much stronger data security. 

But this server still can be vulnerable if there is a disruption to your database. 

Today, we’ll show you how to plan for a SQL Server disaster recovery to protect your database from any kind of data loss in events like equipment failure, cyber attack, or natural disaster.

What is SQL Server Disaster Recovery Anyway?

A SQL Server disaster is any event that causes loss of data or a serious SQL server disruption that can be caused because of unpredictable events like hardware or programming failures, manual errors, cyberthreats like malware and viruses, and issues in a SQL architecture. SQL Server disaster recovery is the process of ensuring the SQL Server stays up and running by recovering or resuming the services from another geographical location to overcome data loss.

How SQL Server Disaster Recovery Works

The main goal of SQL Server disaster recovery is to ensure business continuity whenever disaster strikes. To do this, however, you’ll need a complete plan that includes all dependencies and can help protect against disaster.

Not all disaster recovery plans are the same, and nor should they. You must tailor your SQL Server disaster recovery plan to meet your organization‘s specific data protection requirements. For example, data driving mission-critical financial apps are a greater priority and need immediate recovery than, say, data that you need to create marketing and sales reports.

What’s more, your disaster recovery plan must be as simple and effective as possible. To prepare an effective SQL Server disaster recovery plan, you need to determine the following three metrics:

  • Recovery Time Objective (RTO): RTO is the maximum amount of time an app can be offline because of unavailable data. It tells you how quickly data needs to be restored back online after a disaster. This metric depends on the backup size and type, with full backups taking longer to restore than differential backups.
  • Recovery Point Objective (RPO): RPO is the acceptable amount of data loss your organization can tolerate if a data loss event takes place. Interestingly, this metric is considered in terms of time. So if you backup your database every three hours and a disaster takes place right before the next scheduled data backup, all data changes made between the last backup and the time of disaster will be lost.
  • Recovery Level Objective (RLO): RLO is the level of granularity at which your data should be recovered. This can include table level, database level, or instance level.

The shorter the RTO and RPO in terms of time and the finer the RLO granularity, the greater your costs of implementing a disaster strategy.

Most of us don’t have the luxury of an unlimited budget. If this is you, you should consider hardware costs, storage costs, and licensing costs of the solution. In case you are looking at multiple locations, you’ll need to factor in those costs as well.

Once you have an estimate in hand, factor in the likelihood of a disaster happening. How likely is it that you have a major description over the next year — or perhaps the next 2 to 3 years? Look at the industry and consider trends. Be sure to assess all risks carefully before making a final decision.

6 Strategies for SQL Server Disaster Recovery

After determining the level of protection your organization needs, you can use the following six SQL server backup options to mitigate the impact of sudden disruptions: 

1. Backup and Restore Databases

The backup and restore database technique is a basic option for disaster recovery assurance. 

In this case, you first take a SQL Server backup before copying it to an HA (High Availability) site/server or DR (Disaster Recovery) site/server. Since you can’t do this in real-time, you need to be ready to put in a lot of effort and time. 

Remember, your backup strategy defines the backup type (Full backup, differential backup, transaction log backup, partial backup) and frequency, how backups get tested, and where and how backup media gets stored. On the other hand, your restore strategy defines who handles performing the restores and how many restores you need to perform to meet availability and data loss goals.

To lower potential data loss risks to meet your RPO requirements, schedule a full backup for all production databases and monitor its successful execution. You can also implement a differential backup along with the full backup if the databases have a higher volume to meet RTO expectations.

Consider the following pointers when creating a backup schedule:

  • For all user databases, have a transactional log backup in place. Differential backup can also be added if the database is larger in size and the size of the full backup is massive.
  • For all system databases, do a full backup once every day of the week.
  • Have the store verification process/plan for all database backups and ensure it’s performed frequently.
  • Move database backups to network shares or shareholders instead of placing them in the same server to avoid potential risks of data loss due to sudden disasters.

2. Use Failover Clustering

The concept of failover clustering is simple: a SQL Server instance is installed on the shared storage. 

Essentially, this technique helps in disaster recovery through geo-clustering with different cluster nodes that are placed at different physical locations (or regions). The instance provides the infrastructure to support host server applications. In case a cluster node fails, all services hosted on that node will be automatically or manually transferred to another available node, which is known as the failover process. 

3. Use Always-On Availability Groups

The always-on availability group feature replicates each database transaction on another SQL instance, configured as a failover cluster or in standalone mode, to enable database-level protection. 

Each availability group comprises a group of databases that failover together to a secondary instance. A SQL server can support up to eight sets of corresponding secondary databases in every individual availability group. Within each group are transactions of each database that are applied to a replica database on another SQL server instance.

In the event of a disaster, always-on availability with multi-site implementation switches over to the secondary data centers in another geographical location, allowing site resilience and automated disaster recovery.

4. Use Database Mirroring

If you want to increase the availability of a SQL Server database, the database mirroring technique would be the right approach for you.

It maintains two exact copies of a single database, located on different SQL server instances. These two databases together form a relationship known as a database mirroring session where one instance acts as a principal server and the other remains in standby mode, acting as the mirror server.

There are two types of database mirroring:

  • High Safety Mode (Synchronous): Any data changes happening in the principal database is sent across to the mirror database. Once the changes are committed in the mirror database, they will be auto-committed to the principal database. This type of database mirroring is suitable for HA solutions.
  • High Performance Mode (Asynchronous): Any changes taking place in the principal database are committed in the principal database. All committed changes will then be sent asynchronously to the mirror database. This type of database mirroring is suitable for DR solutions across multiple data centers. 

5. Use SQL Server Replication

SQL Server application makes it possible to copy and distribute data and database objects from one database to another—all by keeping these databases perfectly synchronized.

SQL Server application consists of specific terminology:

  • Publisher (Source database instance that publishes data changes to another database)
  • Distributor (Database to log the changes that took place from Publisher database transaction logs)
  • Subscriber (Destination database instance where the data changes captured in the Distributor database will be distributed)
  • Publications (Collection of one or more articles from a database in Publisher)
  • Articles (Database objects involved in Replication, such as tables, stored procedures or functions, views)
  • Subscription (What publication will be received, from which publication, and what schedule data would be replicated)

Also, SQL Server supports three types of replication: 

  • Transactional Replication: Replication agents will monitor changes in the publisher and transmit these changes to the subscribers. 
  • Merge Replication: Publisher and subscriber independently make changes to SQL Server database. The merged agent will then monitor the changes on the publisher and subscriber and, if needed, will modify the databases. In case of a conflict, a predefined algorithm will specify the appropriate data.
  • Snapshot Replication: The publisher will take a snapshot of the entire database, which will then be made available to all subscribers.

You can use the replication method to distribute data to different locations across local area networks (LANs), wireless connections, wide area networks (WANs), and the internet.

6. Use Log Shipping

Log shipping allows admins to automatically apply a database’s transaction log on a primary SQL Server instance to one or more secondary databases on separate instances. 

The transaction log backup received is then restored to each of the secondary databases individually through a Restore Job. You can also have an optional third server instance set up as part of this architecture to monitor and automate the entire process of recording the history and status of backup and restore operations.

Log shipping is a cost-effective technique since SQL Server controls the log files without additional dependencies. Less, there is no requirement to keep synchronized copies of databases in multiple locations in real-time.

Final Thoughts

And that’s it—this is how you create an SQL Server disaster recovery plan that protects your organization against potential data loss from future disasters. 

Remember, no SQL server disaster recovery strategy is perfect. You need to test your RTO against every solution to set up a robust disaster recovery mechanism for SQL administrators.

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Bryan Wise
Bryan Wise,
CIO of GitLab

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