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Dell High Availability and Disaster Recovery Solutions Using Microsoft SQL Server 2012 AlwaysOn

Availability Groups

We validated the configuration outlined in Figure 4 using four PowerEdge R720 servers. Figure 5 shows

the replica configuration window of the New Availability Group wizard.

Figure 5.

Creating AVG with FCI

In Figure 5, MYFCI is name of the FCI (running on either Node1 or Node2) and is configured as the

primary replica with Synchronous-Commit mode. Node3 is configured as secondary replica with

Synchronous-Commit mode in the primary site. Node4 is configured as another secondary replica with

Asynchronous-Commit mode at the DR site. The readable secondary option has been set to "Read-

Intent Only" for all the nodes. The Automatic Failover option has been disabled for MYFCI instance as

automatic failover is not supported when FCIs is implemented with AVG.

Another important setting to be considered is NodeWeight. In order to avoid the impact of failures in

the DR site, we may set the "NodeWeight" parameter of Node4 to zero so that Node4 will not

participate in cluster quorum voting. When we set the "NodeWeight" of Node4 to 0, we may have to

change the quorum configuration to "Node Majority". In this case only first three nodes (on the primary

site) will take part in quorum voting. But this configuration can sustain only 1 node failure.

More configuration details of this setup are shown in Figure 6.

Figure 6.

FCI with AVG deployment setting

As shown in Figure 6, there will not be any data loss as long as the AVG databases are failover/failback

among the Node1, 2 and 3. There may be a data loss, however, when AVG databases are failover to

Node4 in DR site as Node4 is configured as Asynchronous-Commit mode.