Problem
For over two decades SQL Server has supported multiple instances of the database engine on a single server. But is going down this path really worth it? In some situations the answer should be a resounding ‘yes’. When would I want to use them?
Solution
Too often I see beefy SQL Server’s that sitting are idle. Maybe using a fraction of their resources. This is a significant investment in hardware, licensing and time from numerous technical professionals. Setting up multiple instances of SQL Server is simple and can be a significant cost savings. This could be the case across production and lower life cycle environments. A single SQL Server 2025 server can have 1 default instance and up to 49 named instances of the relational engine on a standalone server.
Why SQL Server consolidation?
The sky is the limit when it comes to why you want to use multiple instances. The reasons may be different from organization to organization. Nevertheless, below outlines some common reasons why multiple instances of SQL Server are used.
Licensing Savings
With the cost of licensing rising with each version of SQL Server, running multiple instances of SQL Server can really make the DBAs look like a hero saving real dollars for the department and organization. SQL Server consolidation of Development, Test, QA, departmental and client specific needs are logical means to get started.
Application, Functional or Load testing
Load Testing – Multiple SQL Server instances provide the Ability to have multiple code bases loaded. The team can coordinate stopping the needed instances to perform load testing. Then conduct the load testing. Once completed, restart all of the instances.
Functional Testing – Ability to have multiple code bases and be able to test independently with a pre-allocated number of resources.
Reduce Power Consumption and Space
One of the recent trends is consolidating multiple instances of SQL Server on to a single server to reduce power consumption and data center space. This too can be a significant recurring cost savings. SQL Server consolidation is not necessarily just to benefit the DBAs, but the overall IT organization.
Internal Hosting or Departmental Sharing
With SQL Server originally considered a departmental solution, it is possible to have multiple instances of SQL Server on 1 physical server to equally share the server’s resources (large number of CPUs and memory). This scenario is ideal for charge backs to the departments for organizations following that paradigm.
Security
Multiple instances are ideal for those pesky third-party applications that require elevated SQL Server privileges where you do not want to commingle applications on the same instance.
Compliance
In some industries it is necessary to access older data, perhaps seven years old. This means that could be an older version of SQL Server. By using named instances with the individual versions, service packs, cumulative updates, hot fixes, etc. installed, instances can be started to support the specific restore needs.
Client Specific Instances
Over the years I have seen circumstances where databases and applications are client specific and need to be isolated. Perhaps a specific code base, business requirements, legal regulations, etc. Named instances enable supporting these specific needs at a fraction of the cost of a dedicated server.
Demos
Multiple instances are ideal to support demo’s where it is necessary to demonstrate a particular application and how it affects SQL Server. This could multiple versions of SQL Server to test a variety of applications.
Words of Caution
Evaluate the workloads for each instance to ensure that the final consolidated instances will operate smoothly together. Beyond memory and CPU limitations, play close attention to disk performance and disk space. Ensure there are sufficient resources to realistically support each SQL Server instance and the associated applications.
Be sure to coordinate backups and maintenance so these processes are not all running at the same time and flooding disks.
With security on the forefront of so many people’s minds, we could not help to mention that with multiple instances of SQL Server be sure to update all of the instances, not just the default or first instance. Many of the patches need to be applied per instance and not per server.
Think about security not only at the instance and database levels, but also in the file system if it is not possible to carve out dedicated storage for each instance.
Next Steps
- As you face these issues and others, consider consolidating SQL Servers to help address the issue from a technology perspective.
- Setup a naming convention for your instances. Two broad approaches are to functionally name the instance (i.e. AcctFnctnlTesting, ManufacturingTesting, etc.) or enumerate generic names (i.e. Inst1, Inst2, etc.).
Jeremy Kadlec is a Founder, Editor and Author at MSSQLTips.com with more than 300 contributions and 25+ years of SQL Server experience. Jeremy leads a team of more than 300 authors helping millions of SQL Server professionals around the globe every second of the day for the last 20 years. He is also the CTO @ Edgewood Solutions and a six-time SQL Server MVP based on his community contributions. Jeremy brings 25+ years of SQL Server DBA and Developer knowledge to the community and holds a bachelor’s degree from SSU and master’s degree from UMBC.