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Introductie van Micorosoft SQL Server 2016

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35 C H A P T E R 3 | Higher availability Two replicas (one primary and one secondary) One availability database No read access on secondary replica No backups on secondary replica No availability group listener No support in an existing availability group to add or remove a replica No support for upgrading a basic availability group to an advanced availability group Despite these limitations, with a basic availability group you get benefits similar to database mirroring in addition to other features. For each replica, you can choose either synchronous-commit or asynchronous-commit mode, which determines whether the primary replica waits for the secondary replica to confirm that it has hardened the log. Moreover, performance is better because basic availability groups use the same improved log transport operations that we describe later in this chapter. The steps to configure basic availability groups are similar to those for regular availability groups, with some exceptions. You start by using the New Availability Group Wizard, which you launch in SQL Server Management Studio (SSMS) by right-clicking the AlwaysOn High Availability folder in Object Explorer. When you reach the Specify Replicas page, you click the Add Replica button to add the primary and secondary replicas, but then the button becomes unavailable, as shown in Figure 3-2. In addition, you cannot change the value for the Readable Secondary drop-down list, nor can you access the Backup Preferences or Listener tabs. Figure 3-2: Configuring replicas for a basic availability group.

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