SQL SERVER DRILL DOWN - Fly to the Cloud Using the Azure Database Migration Service (DMS)

On August 30, Microsoft announced the public preview of the Azure Database Migration Service (DMS) to support online migrations of various databases to Azure. What’s an “online migration”? Online migration means that your databases remain operational while conducting the migration. This provides quite a few obvious benefits, such as minimum downtime for critical applications, limited impact to service-level agreements (SLAs), and reduced inconvenience to end users. DMS can be used for both operational databases and data warehouse migrations, running on SQL Server and MySQL. PostgreSQL and Amazon RDS online migrations are coming soon.

How Much Does It Cost?

Spoiler alert—all tiers are currently free during the public preview, including the premium Business Critical pricing tier.

Going forward, there are several General Purpose pricing tiers to support offline migrations, also known as “one-time migrations.” These General Purpose pricing tiers, which offer a selection of 1-, 2-, and 4-vCore options, are generally available and free to customers. The Business Critical pricing tier supports both offline and online migrations, also known as “continuous migration,” for business-critical workloads that require minimal downtime and/or a period of running in parallel. More details about pricing can be found at the Azure Database Migration Service pricing webpage (

How Do Online Migrations Work?

Online migration in DMS are quite simple whether you’re migrating to SQL Server or MySQL. DMS first performs a full data load (basically, an offline migration). DMS then creates a continuous sync with the target databases. The synchronization process runs until you engage the cutover migration at a time that’s convenient. I recommend that you watch the short videos for your database platform(s) of interest before you get started:

There are a number of prerequisites and considerations before you get rolling. For example, the source SQL Server database should be SQL Server 2005 or greater. Review these checklists before performing your first migration:

You might also want to spend a few minutes strictly studying the tool and how to perform a SQL Server Migration assessment. This step of the process not only detects compatibility issues and feature parity when migrating the database schema, it can also recommend new features in the latest release of SQL Server that you can take advantage of which you might previously have missed. This can be especially useful if the database you’re migrating is “vanilla” and only uses the most common features of a relational database. DMS might recommend features to you that enable significant performance improvements!

Incidentally, if you haven’t checked in on Azure Database for MySQL, a variety of new features and improvements were announced on July 12. New features include large database support (up to 4TB), data-in replication, geo-redundant backup and recovery, and memory-optimized SKUs. You can catch up on the newest features at

There’s also a very handy resource that I recommend—Database Migration Guide: Step-by-step guidance for modernizing your data assets available at

Who Can Use the Public Preview?

The public preview of DMS will roll out in a piecemeal fashion by region. The initial regions that can take immediate advantage of DMS include:

  • Central US
  • East US2
  • West Europe

The rollout supports online migrations for these scenarios:

  • On-premise SQL Server and SQL Server on IaaS to Azure SQL Database
  • On-premise MySQL and MySQL on IaaS to Azure Database for MySQL

Other Azure regions and deployment scenarios will come online soon.

Where Can I Learn More?

The best place to get additional information are the Microsoft MSDN blogs of the R&D teams themselves. You can read the release announcement from the team developing the SQL Database online migration feature here:

The blog announcing the release of MySQL online migration feature is posted here:

And the How-to guide: Monitor online migration activity is posted here: