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| How application availability is achieved in a physical environment | ||
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| How application availability is achieved in a physical environment | ||
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| Prev | Understanding the InfoScale solutions for application high availability | Next |
The VCS agents continuously monitor the application, storage, and network components that the application uses in the cluster. The agents are able to detect failures in all of these components. For example, an application-level failure such as a configured application virtual server or application service becoming unavailable, a fault in the storage such as a configured disk becoming inaccessible, or a network failure.
When a fault occurs, VCS fails over the application service group to the next available system in the application service group's system list. A service group failover means that the VCS storage agents deport and import the disks or LUNs on the new system. The VCS network agents bring the network components online and the application-specific agents then start the application services on the new system.
In a disaster recovery cluster configuration, VCS first attempts to failover the application service group within the local cluster. If all the systems in the local cluster are unavailable, VCS attempts to failover the service group to a system at the remote site.
In a NetApp environment, the VCS NetApp agents perform the following actions in that order:
Connect the virtual disks (LUNs) to the target hosts (NetAppSnapDrive agent).
Perform a mirror break that enables write access to the target (NetAppSnapMirror agent).
Reverse the direction of replication by demoting the original source to a target, and begin replicating from the new source (NetAppSnapMirror agent).
If replication is set up using Volume Replicator (Volume Replicator), the Volume Replicator replication agents make the Secondary RVG at the remote site write-enabled so that it becomes the new Primary. After the storage is connected, VCS starts the application services on the new system at the remote site. The data that is replicated to the remote site is used to restore the application services to the clients.