What’s the Difference Between Data Replication and Database Mirroring?

If you’re looking into options for expanding your systems’ capacities or making your database accessible outside of the systems where it’s produced, you’ve probably come across the terms database mirroring and data replication.

Taken at face value, these processes sound somewhat similar. So, what’s the difference? Aren’t both processes simply ways to copy data?

Of course, there’s more nuance to it than that. While data replication and database mirroring do both involve the copying of data, they are markedly different processes that are meant to achieve different results for different purposes.

Let’s dive in to identify the distinctions.

Definitions of Database Mirroring and Data Replication

These two processes are somewhat similar, but by definition they have several key differences.

Data replication is concerned only with the replication of the content of database tables (which we call the data), and any associated layout information that’s necessary for understanding the context of that data (which is called schema information). Often, data replication involves replicating only a subset of the data from the source database.

Database mirroring, on the other hand, involves the replication of an entire database management system (DBMS). This involves more than the data and schema information; it also includes information like security credentials, authorities, program extensions (such as stored procedures), user-defined functions, triggers, and other related objects such as indices, constraints, and so on.

To illustrate: Database mirroring would be akin to duplicating the entirety of a website – its fonts, styles, colors – to the point that the copied website would be virtually indistinguishable from the original. Accordingly, database mirroring results in the creation of another, identical database.

Data replication would be akin to duplicating only the written content of the website. The process involves picking and choosing the relevant information to copy.

Different Deployment Considerations

Given the different definitions of database mirroring and data replication, it follows that they would be deployed differently.

Database mirroring is deployed in homogeneous environments where the database products are identical. It’s really only possible to fully mirror a database if the environment it’s being mirrored in is the same as the source environment; otherwise, some of the database material will inevitably be lost.

Data replication is more common in heterogeneous environments. While it’s possible to replicate data to a homogeneous destination, the process works well between unlike database products, and so it tends to be most commonly used for that purpose.

Different Use Cases

Finally, with the definitions of the terms outlined and their deployment considerations understood, let’s take a look at what each process is used for.

Database mirroring is often used for:

Load balancing. In situations where organizations need access to multiple copies of data for performance reasons, database mirroring can be helpful. It’s a horizontal scaling method that can allow systems to achieve greater capacity.

Disaster recovery (specifically high availability). This is another prime use case for database mirroring. Disaster recovery is normally taken to mean a complete loss of a system – perhaps a facility goes down or a location crashes, requiring a failover to a remote location. Database mirroring can provide redundancy in these instances.

However, it’s perhaps most useful for high availability scenarios – situations where an organization needs to maintain functionality if a portion of capacity is lost. In these contexts, if a single host computer or a disk goes down, the mirrored database allows the organization’s systems to continue functioning normally.

Data replication is often used for:

Making information available outside of the system that’s responsible for producing or maintaining it. For example, a bank system might maintain ledgers of account information. That’s the system of record for the bank; it represents customer activities, transactions, and so forth.

When customers get their statements, they’re getting them via a form of data replication; they’re seeing a portion of that system of record at a certain point in time as it pertains to their particular view of the data.

They don’t get to see the entire capital structure or the personnel information of the bank – they don’t access the entire database. What they see is very specific information as it pertains to their needs. The system that generates their statement is completely different, perhaps, than the systems that the bank uses to maintain all of its other information.

The reasons to choose data replication may be based on performance or security or logistical reporting, but the key similarity is that access to data is needed outside of the systems in which the data is produced and maintained.

Ready to implement a database mirroring or data replication solution?

Hopefully, the information above has helped you to clarify the differences between these two processes.

If you’re ready to move forward with a data replication or database mirroring solution, get in touch with us.

At StarQuest, we’re experts at data replication and database mirroring. Our powerful SQDR software can be utilized for replication from an extensive range of data sources, and it powers real-time change data capture using a log-based approach.

And, importantly, our customer service team is regarded as some of the best in the business, with clients calling us “The best vendor support I have ever encountered.”

Get in touch with us to discuss your data access needs. We can set you up with a no-charge trial of our software using the DBMS of your choice, and help you take the first step toward a solution that will benefit your business.