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SQL Server Distributed Availability Group Migration Guide

Blog post from Tessell

Post Details
Company
Date Published
Author
Priyank Parikh
Word Count
2,535
Company Posts That Month
12
Language
English
Hacker News Points
-
Post removed?
No
Summary

A Distributed Availability Group (DAG) is a specialized SQL Server feature that connects two distinct availability groups across different clusters, enabling seamless data replication without a shared Windows Server Failover Cluster (WSFC). Introduced in SQL Server 2016, DAGs facilitate cross-cloud migrations, version upgrades, and disaster recovery by allowing continuous data replication between source and target environments, such as on-premises to cloud platforms like Tessell. Unlike traditional Always On Availability Groups, which require a single WSFC, DAGs operate independently across various data centers, clouds, or domains, using a two-tier forwarding model to efficiently manage log streams. This approach eliminates cluster boundary constraints and supports scenarios where environments cannot share a WSFC, making it ideal for large-scale SQL Server migrations with minimal downtime and near-zero data loss. The migration process involves provisioning the target, establishing the DAG with either automatic or manual seeding, and executing a controlled failover after ensuring synchronization, with post-migration tasks such as re-enabling Tessell triggers and updating application connection strings to complete the transition.

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