A synchronization group is two or more databases that are logically grouped together for the purpose of synchronizing specified tables, columns and rows common to each. A sync group must have a SQL Azure hub database through which all synchronizations pass.

This article walks you through how to add the SQL Azure hub database to the sync group.

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Prerequisites

1. Provisioned a SQL Azure Data Sync server - SQL Azure Data Sync Provision a SQL Azure Data Sync Server 

2. Named the sync group -  SQL Azure Data Sync Name a Sync Group 

3. See the article SQL Azure Data Sync Create a Sync Group for the flow of all the steps to create a sync group.

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Add a SQL Azure Database as the Hub

SQL Azure Data Sync uses a hub/spoke topology. The hub is the central database in a Sync Group and must be a SQL Azure database. It is best if the hub is either (a) in the same data center (when databases are not geographically disbursed) or, (b) in the location most central to the other databases. The two most significant factors in selecting a hub database is latency and cost. Choosing a hub database that is close to the majority of your data traffic minimizes both latency and cost. Once the hub is set, it cannot be changed to a different database or removed. Data changes in member databases are written to the hub database or discarded in accordance with the Conflict Resolution policy. After all the member databases have sent their changes to the hub, the hub then write changes to all the member databases.

1. Click the add SQL Azure database as Hub icon. (Figure 1)

   
   Figure 1: Add a Hub Database

2. Enter or select from the dropdown the database SQL Azure server name. (Figure 2:1)

3. Enter or select from the dropdown the database name. (Figure 2:2)

4. Enter your Credentials. (Figure 2:3)

5. Click Test to confirm that the server name, database name, user ID and password are all correct. (Figure 2:4)

6. If the test is successful, click Add. (Figure 2:5)

   
   Figure 2: Add a SQL Azure database as the Sync Group Hub

   Note: If, when you click Add, you get an Error saving the database to server dialog the problem may be the firewall settings on the server. Return to the Windows Azure Management portal. In the left pane click the Database add-in. In the tree view of subscriptions and servers select the server. Ensure that the Allow other Windows Azure services to access this server checkbox is checked.

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See Also

• SQL Azure Data Sync Overview
• SQL Azure Overview

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