Avg deployments on shared storage – Dell POWEREDGE R720XD User Manual
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Dell High Availability and Disaster Recovery Solutions Using Microsoft SQL Server 2012 AlwaysOn
Availability Groups
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Limitations:
Limits on storage scalability.
No enhanced SAN capabilities.
AVG deployments on shared storage
In addition to the failover capability provided by AlwaysOn Availability Group, we may also set up a
secondary layer of availability at the server instance level. This is done by implementing SQL Server FCI
together with the underlying WSFC cluster. FCI is configured with shared storage to host the SQL server
instances.
FCIs are basically designed to provide High Availability at instance level whereas AlwaysOn Availability
Group (AVG) is designed to provide HA and DR capabilities at database level.
- Consider the following when you plan to combine the FCI with AVG.
AVG alone does not require shared storage, but when we use FCI to host one or more
availability replicas, each of the nodes which are part of FCIs will require shared storage as per
standard SQL Server failover instance installation.
An FCI may be used together with an availability group to enhance the availability of an
availability replica. However, to prevent potential race conditions in the WSFC cluster,
automatic failover of the availability group is not supported to or from an availability replica
that is hosted on a FCI.
Since SQL Server FCIs do not support automatic failover by availability groups, any availability
replica that is hosted by an FCI can only be configured for manual failover.
All the prerequisites and restrictions that need to be addressed before proceeding with AVG
deployment may be found at
Care should be taken to make sure all the specified
hotfixes are installed on the appropriate nodes.
Figure 3 shows the typical AVG deployment along with SQL Server FCI.