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A SQL Server disaster recovery plan is not a technical document, it is a business survival plan. Disaster recovery is the set of processes and infrastructure that enables the restoration of your SQL Server databases and applications to a working state following a catastrophic event. A disaster recovery plan helps in business continuity and database recovery in SQL Server . This guide will give you a complete end-to-end methodology to design, build, test, and maintain disaster recovery solutions in SQL Server.
Common Causes of SQL Database Disasters
Before going further, let us list the factors which could lead to disaster in SQL Server and affect its working.
- Hardware failures
- Sudden power outages
- Programming failures
- External threats like malware and viruses
- Corruptions in the database
- Manual errors
- Issues in SQL architecture
- Low disk space
- Silent agent job failure
- Deadlocks and concurrency storms
SQL Server Disaster Recovery Plan: Detailed Stepwise Information
Here is the detailed SQL Server disaster recovery plan which every IT Admin or individual should follow:
Step 1. Set Your Recovery Target First
Below are the three pillars of the disaster recovery plan. These are used in SQL Server and at the time of DR planning:
- Recovery Time Objective (RTO): How much downtime can your system tolerate?
- Recovery Point Objective (RPO): How much data can you afford to lose?
- Recovery Level Objective (RLO): What level of recovery do you want to achieve?>
This is how long your organization can operate without this system and still consider it a business function.
This is the maximum acceptable data you can afford to lose in a disaster.
Server level recovery? Database level recovery? Table level recovery? Single row level recovery?
Step 2. List The Disaster You Are Planning For
A comprehensive disaster recovery plan should account for all scenarios at all levels. This includes:
- Server or disk failure
- Database corruption
- Ransomware or malicious deletion
- Site or region outage
- Human errors, such as a dropped table or bad UPDATE
Step 3. Choose The Technology
The in-built disaster recovery options provided by the Microsoft SQL Server are:
- Taking Database Backups Regularly
- Using Always-On and Basic Database Availability Groups
- Log-Shipping
- Fail-over Clustering
- Database Replication
I guess most of the administrators are aware of this option although they don’t take it seriously. Let us know what an administrator can do for the disaster recovery:
- Database backup through PowerShell, SQL Server Management Studio or using T-SQL backup commands
- Utilize compression as well as encryption while performing a database backup
- Perform 3 four types of database backup:
- Restore database from backups when needed
Full Database – It is a complete backup of the database.
Differential Database – It is the backup of what has changed after the full backup
Partial Database – It covers the primary filegroup plus read/write filegroups
Transaction Log Files – Backup of log files. Done frequently.
Technology 2. Using Always On and Basic Availability Groups
SQL Server Enterprise Edition facilitates Always-On Database Availability Groups technology which protects SQL databases and can perform automatic failover. With Basic Availability Groups in Standard edition (available since SQL Server 2016), an administrator can protect a single database. Let us know how it works:
- Always-On Availability Groups works with Windows Server Failover Clustering on Windows and with Pacemaker on Linux.
- It offers synchronization with secondary replicas and also asynchronous with secondary replicas for disaster recovery.
- Users can keep copies of the primary database on one or more secondary replicas, which can be on more than one system. Each secondary is initialized from a backup of the primary database restored on it, or by automatic seeding.
- Once the Always-On Availability Group is started, it sends all the primary database transactions log records to the secondary replicas.
- Basic Availability Groups work in a similar way to protect SQL databases, but with limitations: no readable secondary replica, and no backup or integrity checks on the secondary.
- Basic Availability Groups provides options like synchronous replication or asynchronous replication.
- These groups work for a single database with one primary replica and one secondary replica (though there can be multiple Basic Availability Groups on a single server, one per database).
Technology 3. Log-shipping procedure
Log-Shipping is available in the Standard and Enterprise editions of SQL Server, including SQL Server 2017, not in the Express edition. An administrator can use T-SQL scripts and SQL Agent jobs to perform the same functions. Let us know it’s working:
- In log shipping, the administrator takes backup of the transaction logs on the primary database.
- Then copy this backup to one or more than one secondary database.
- Now, restore the transaction log backup on the secondary SQL server.
- SQL administrators can decide the time intervals between transaction logs of the primary server, the copy, and the restore on secondary server.
Technology 4. Fail-over clustering
Always-On Fail-over Clustering Instances facilitates server protection from server failure. It helps in disaster recovery through geo-clustering with cluster nodes placed at different physical locations (can be in different regions too). Let us understand it more:
- Works on Windows Server with Windows Server Failover Cluster and on Linux with Pacemaker.
Supported by SQL Server 2017 Standard and Enterprise editions but with nodes limitations on Standard (2 nodes are allowed). - In this procedure, the administrator installs a SQL Server instance across the cluster nodes, with its databases on shared storage.
- An infrastructure is developed with different cluster nodes (the active nodes and the passive nodes) connecting to the shared storage, while clients connect through the cluster’s network name.
- Whenever any cluster node fails, the services hosted on that node can be automatically or manually transferred to another node which is known as failover.
Technology 5. Database replication
This procedure involves copying SQL Server database data and then distributing it to another database. Replication is mainly meant for distributing data, so it supplements a disaster recovery plan and doesn’t replace backups or availability groups. Let us go through some important points about it:
- Replication technology consists of Publisher, which are is the database that deliver makes data available; a Distributor, which stores and forwards the changes, and Subscribers, which are databases receiving database from the Publishers.
- Any modification in Publishers gets automatically updated to Subscribers according to the replication type (snapshot, transactional, or merge). with synchronization
- It can offload read workloads by distributing data to a number of servers.
Step 4. Step-by-Step Failover Runbook
A proper disaster recovery solution in SQL server must include a step-by-step documentation manual (runbook) accessible even if primary corporate systems are down. It should include:
- Make sure Active Directory/Domain Controllers and DNS are fully operational in secondary recovery sites.
Perform forced manual failover to the asynchronous secondary target (For AGs) or restore final tail-log backup, or bring standby database online using RESTORE DATABASE WITH RECOVERY. - Update DNS or redirect SQL Server Listener IP address so that it routes to a secondary cluster.
- Start web servers and applications only after the database engines are verified and fully online.
Step 5. Testing and Monitoring
- Conduct Regular Test Failover: A disaster recovery plan is only as good as its last test. Perform isolated network failover drills at least semi-anually to validate data integrity and timing metrics without impacting the production system.
- Optimize Licensing Costs: Microsoft provides free passive replica instances for business continuity without requiring additional core licenses.
When Native Restore Fails: What to Do Next?
Most of the time, the standard restore process works fine. But a few times, we have to run into situations where the .bak file itself is corrupt or the database shows unexpected errors. So, a SQL Database Recovery tool would be the last resort when no good backup exists. Kernel SQL Database Recovery tool has a simple user-interface and works for all the SQL Server versions. It comes with a free trial version which allows users to test the features and functionalities before purchasing the licensed version.
Last Say
Some disaster recovery options in SQL Server (using Microsoft SQL Server in-built features) are discussed to help you recover from avoid any sort of future disasters (human-made or natural) that can lead to SQL data loss. Regular database Backups are the foundation of these plans. But if no usable backup exists and you need to recover corrupt and damaged MDF files or recover deleted records in SQL server , Kernel SQL Database Recovery can help.
Frequently Asked Questions
Ans. Disaster recovery in SQL works by maintaining secondary copies of the database either through automated live replication, continuous log updates, or traditional backups.
Ans. The fundamental difference is that RTO (Recovery Time Objective) measures acceptable downtime and RPO (Recovery Point Objective) measures acceptable data loss.
