Exploring the Differences Between Always On Availability Groups and Distributed Availability Groups (DAGs) in SQL Server

-

 

 

 A distributed availability group (AG) is a special type of availability group that spans two separate availability groups. Distributed availability groups are available starting with SQL Server 2016.

The availability groups that participate in a distributed availability group don't need to be in the same location. They can be physical, virtual, on-premises, in the public cloud, or anywhere that supports an availability group deployment.

The following figure shows a high-level view of a distributed availability group that spans two availability groups (AG 1 and AG 2), each configured on its own WSFC. The distributed availability group has a total of four replicas, with two in each availability group. Each availability group can support up to the maximum number of replicas, so a distributed availability can have up to 18 total replicas.

 

 

 However, data movement is slightly different within distributed availability groups compared to a traditional availability group. Although each availability group has

a primary replica, there is only one copy of the databases participating in a distributed availability group that can accept inserts, updates, and deletions.

As shown in the following figure, AG 1 is the primary availability group. Its primary replica sends transactions to both the secondary replicas of AG 1 and the primary replica of AG 2. The primary replica of AG 2 is also known as a forwarder. A forwarder is a primary replica in a secondary availability group in a distributed availability group. The forwarder receives transactions from the primary replica in the primary availability group and forwards them to the secondary replicas in its own availability

 



The only way to make AG 2's primary replica accept inserts, updates, and deletions, is to manually fail over the distributed availability group from AG 1. In the preceding figure, because AG 1 contains the writeable copy of the database, issuing a failover makes AG 2 the availability group that can handle inserts, updates, and deletions.

Comments

Post a Comment

Popular posts from this blog

Interview Questions on AOAG

-
1.What are the prerequisites for setting up AlwaysOn? 2.How do you set up replication in AlwaysOn environment? 3.How do you manage replication during Windows patching or failover if replication has been set up in AlwaysOn? 4.How do you sync logins in AlwaysOn? 5.How do you sync users in AlwaysOn secondary? 6.How do you add database files in AlwaysOn? 7.How do you perform an in-place upgrade of SQL Server in a AlwaysOn environment? 8.What is the procedure for SQL Server patching in AlwaysOn? 9.How do you failover a mirror server if replication has been set up? 10.What is the SPN concept in AlwaysOn? 11.What is file share in AlwaysOn? 12.How do you create multiple AlwaysOn listeners? 13.How do you check latency in AlwaysOn? 14.What is the command used to check latency in replication without using GUI? 15.What are DNS issues in AlwaysOn? 16.If a user is connecting to the primary and not able to connect to the secondary, and the secondary is in read-only mode, how do you fix the issue in A
Read more

Database Administrator Designations

-
  Database Administrator Designations: Exploring Key Roles and Responsibilities In today's data-driven world, the role of a Database Administrator (DBA) is crucial to ensuring that data is stored, managed, and accessed efficiently and securely. Within the realm of database administration, there are various specialized roles, each with distinct responsibilities and skill sets. Let's delve into the key designations in database administration and understand what each role entails. 1. Database Administrator (DBA) Responsibilities: Database Installation and Configuration: Setting up new databases, including installing database management systems (DBMS) software. Backup and Recovery: Creating and managing backup strategies to ensure data can be restored in case of loss or corruption. Performance Tuning: Monitoring and optimizing database performance, including tuning queries and managing indexes. Security: Implementing security m
Read more

Interview questions for Junior SQL server DBA.

-
  1.        What is SQL Server build? 2.        What are the system DBs available in SQL Server, and what is the significance of each DB? 3.        How will you troubleshoot a log file growth issue that is causing disk space issues? 4.        What are startup parameters? 5.        What are the DBCC commands you use regularly? 6.        What are the DMVs you know, and what is the purpose? 7.        How will you troubleshoot blocking? 8.        What is the difference between locking and blocking and deadlock? 9.        What is the tail log backup, and when will it be useful? 10.    How does SQL Server identify differential backups? 11.    How will you verify logins and users using queries in SQL Server? 12.    What are the differences between mirroring and log shipping? 13.    Can we configure mirroring in bulk log recovery model? 14.    Can we configure log shipping in bulk log recovery model? 15.    What is the quorum drive, and what is the use of it? 16.
Read more