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[1] Azure Tips and Tricks: SQL migration to Azure with near-zero downtime

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Context:

You need to do a migration from an on-premises SQL Server 2019 instance to Microsoft Azure. There are 3 databases that need to be migrated, each of them has around 3-4 TB. The migration plan includes an Azure SQL Database Managed Instances.

Problem:

The challenges are around the data loss during migration and how to minimize the downtime. 


Solution

The first thing that you need to do is to include DMA (Database Migration Assistant) during the migration assessment. It would allow you to identify any compatibility issues between on-premises and Azure. Additional, DMA is able to provide a list of actions that can be done on the destination environments to do reliability and performance improvements. 

The migration of the schema, data, and uncontained objects can be done using DMA. Allowing to have a migration plan with near-zero downtime. 

On top of it is mandatory to consider DAG (Distributed Availability Groups) for the managed instances, which would enable you to have a strong DR (Disaster Recovery) plan. Think twice if you really need DAG versus the out of the shelve backup and replication capabilities offered by SQL in Azure.

At this moment in time configuration of DAG is done only from the command line and you need to be well documented. Why? Because it involves creating WSFC clusters, AG (Availability Groups) for each WSFC, an ILB (Internal Load Balancer), and configure in the write way the AG endpoint (port 5022 for SQ). Don't forget about port 1433 and 5022 that needs to be available between the clusters. 

The documentation is pretty well, but with testing, it will require you 2MD for the full configuration and testing of DAG.


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