You read an AZ-305 scenario about moving on-premises SQL Server databases to Azure, and two answer options both look reasonable. The one that wins is the lifecycle stage in the stem. Azure Migrate discovers the estate, assesses readiness, and recommends the Azure SQL target. Azure Database Migration Service (DMS) moves the data after the target is chosen. If the scenario is still deciding where the databases should go, the answer is Azure Migrate. If the scenario names the target and the problem is moving the data inside a downtime window, the answer is DMS.
AZ-305 measures this boundary inside the Design migrations tasks of the Design infrastructure solutions domain, which is 30-35% of the exam (skills measured as of April 17, 2026) (AZ-305 study guide). The tasks the boundary maps to are "Evaluate on-premises servers, data, and applications for migration" and "Recommend a solution for migrating databases". The English version of the exam was updated on April 17, 2026, so recheck the study guide before you book (AZ-305 exam page).
The cues that pick each tool
The stem gives you the stage. Read the verb and whether the target is already named, and the tool follows.
Pick Azure Migrate when the stem says discover, assess, readiness, sizing, cost estimate, dependency, or recommend a target. Microsoft describes Azure Migrate as the service that helps you decide on, plan, and execute the migration, and its plan phase covers Azure readiness, right-sizing, and cost estimation (Azure Migrate overview). For a SQL Server estate, the Azure SQL assessment in the Azure Migrate: Discovery and assessment tool recommends an Azure SQL configuration and a monthly cost estimate from configuration data, such as cores allocated, total memory, and database sizes, or from collected performance data, such as CPU usage, file IO, and memory usage (Assess SQL instances tutorial). The assessment covers three targets, Azure SQL Database, Azure SQL Managed Instance, and SQL Server on Azure VMs.
Pick DMS when the stem says migrate, replicate, online migration, offline migration, cutover, downtime window, or move the data to a named target. Microsoft describes DMS as a fully managed service for migrating from multiple database sources to Azure data platforms with minimal downtime on online migrations, available through the Azure portal, PowerShell, and Azure CLI (DMS overview). For SQL Server sources, the documented floor is SQL Server 2008 and later, and DMS does not store customer data during the migration (DMS FAQ).
The target test. If the target is still open, the question is about assessment and Azure Migrate is in play. If the stem names the target, the question is about execution and DMS is the tool in play.
What each tool does, per the service pages
Azure Migrate is the hub. The overview describes it as a free service that covers discovery, assessment, and migration across servers, databases, web apps, virtual desktops, and offline data movement with Azure Data Box (Azure Migrate overview). For databases, the overview says the hub can assess on-premises SQL Server instances and databases to migrate them to SQL Server on Azure VMs, Azure SQL Managed Instance, or Azure SQL Database. DMS runs the move to those targets as a separate service, and its feature table marks migration Yes for all three (DMS overview). The assessment and the move are separate tools, and the exam treats them the same way.
DMS is the execution side. The DMS overview feature table for the DMS (Azure portal) experience marks Assessment as No and SKU recommendation as No, and marks migration Yes for Azure SQL Database offline, Azure SQL Managed Instance online and offline, and SQL Server on Azure VMs online and offline (DMS overview). Two consequences for the exam. First, a stem that asks the tool to choose or recommend the target is outside DMS, because the service page marks those jobs as not provided. Second, online mode, where downtime is limited to the cutover at the end of the migration, exists for Azure SQL Managed Instance and SQL Server on Azure VMs. To Azure SQL Database, DMS runs offline, and application downtime starts when the migration starts (DMS FAQ).
The DMS FAQ draws the same boundary. Asked how DMS compares to the Azure Migrate offering, it answers that Azure Migrate is useful for lift-and-shift migrations of VM-based workloads to Azure IaaS and "isn't a specialized database migration service offering for Azure PaaS relational database platforms such as Azure SQL Database or Azure SQL Managed Instance" (DMS FAQ). The FAQ frames Azure Migrate by what it does not execute, and the overview frames it as the hub that includes the SQL assessment. Both statements are true at their level, and together they state the exam boundary plainly. Azure Migrate owns the evidence before the move. DMS owns the move.
The comparison, with the verdict row
| Azure Migrate | Azure Database Migration Service | |
|---|---|---|
| Lifecycle stage | Decide and plan, before the move | Execute, the move itself |
| What it produces | Discovery, readiness, right-sizing, cost estimate, and a target recommendation among Azure SQL Database, Azure SQL Managed Instance, and SQL Server on Azure VMs | The migration itself, schema and data moved to the target you chose |
| Assessment and SKU recommendation | Yes, in the Azure SQL assessment | No, on the DMS (Azure portal) experience |
| Downtime handling | Cost estimation, not cutover | Online, downtime limited to the cutover, to Azure SQL Managed Instance and SQL Server on Azure VMs; offline only to Azure SQL Database |
| Available through | The Azure Migrate portal, a free service | The Azure portal, PowerShell, and Azure CLI |
| Verdict | The stem is still choosing a target | The stem is moving data to a named target |
Where the rule bends
Minimal downtime with an Azure SQL Database target. DMS supports online migration only to Azure SQL Managed Instance and SQL Server on Azure VMs, and online mode requires a DMS instance based on the Premium pricing tier. To Azure SQL Database it is offline only, and application downtime starts when the migration starts (DMS FAQ). A stem that pairs "minimal downtime" with an Azure SQL Database target is therefore not a DMS online answer.
"Assess" inside a DMS workflow. The DMS FAQ's step list for running a migration includes assessing the source databases with SSMA, which can also convert database objects and migrate the schema (DMS FAQ). That step clears the way for the execution. It is not the design-stage assessment the study guide tasks describe. A stem that asks you to evaluate the estate and recommend where it should land is answered by the Azure Migrate SQL assessment. A stem that describes running the DMS migration workflow is answered by DMS.
Old material that names Azure Data Studio. Azure Data Studio is retired as of February 28, 2026, and Microsoft says the dedicated migration tooling for each target replaces the Azure SQL migration extension that shipped in it (Azure Data Studio retirement). If your study material recommends the Azure Data Studio migration extension, treat that line as stale and answer with the current DMS portal, PowerShell, or CLI path.
Adjacent tools. SSMA does the source assessment and schema conversion inside the DMS workflow (DMS FAQ). Data Migration Assistant (DMA), the standalone SQL assessment tool, is retired from July 16, 2025, and its overview page links to the SQL Server to Azure SQL migration overview for current options (DMA overview).
How the answer flips when the stem changes
Suppose a company has 80 on-premises SQL Server databases. The architecture team wants to modernize, but it does not yet know which databases fit Azure SQL Database, which need Azure SQL Managed Instance, and which should stay on SQL Server running on Azure VMs. Leadership wants a cost estimate before approving the first wave. The right first tool is Azure Migrate. The requirement is assessment. Discover the estate, evaluate readiness, find the blockers, recommend a target per database, and produce the cost estimate. DMS is premature here, because no target or execution path is approved yet.
Now change the stem. The same company completed the assessment, selected Azure SQL Managed Instance for a business-critical database, and needs the move with minimal downtime. The answer shifts to DMS, run through the Azure portal, PowerShell, or Azure CLI. The online path to Azure SQL Managed Instance is the mode that limits downtime to the cutover (DMS overview).
Put the two stems side by side and the boundary is the difference. Azure Migrate answers what you have, where each database should go, what blocks the move, and what it costs. DMS answers how you move this database to the target you already chose.
What to do when you miss this boundary
When a question on this boundary comes back wrong, classify which side of the boundary the miss came from. Target selection or readiness assessment points to the Azure Migrate side. Execution mode, downtime, or cutover points to the DMS side. Take ten mixed migration scenarios, write the lifecycle verb and the target status for each, and check the tool it points to before you look at the answer.
When you want the gaps named across the whole exam, take the free AZ-305 assessment. It is free and needs no card, and it returns a Readiness Report with your top gaps (take the free AZ-305 assessment).