What a cluster is

You can group pairs of nodes together to form a scalable cluster. Creating a cluster enables up to 24 individual nodes (or twelve pairs of nodes) to pool their resources and distribute work across the cluster, while presenting administrators with a single entity to manage. Clustering also enables continuous service to end users if individual nodes go offline or are taken offline.

Each node in the cluster can access the same volumes as any other node in the cluster. The total file-system namespace, which comprises all of the volumes and their resultant paths, is global across the cluster.

When a new node is added to a cluster, there is no need to update clients to point to the new node. The existence of the new nodes is transparent to the clients.

A key concept in the cluster is quorum, which is a simple majority of nodes that participate in the cluster. Each node in the cluster participates in a voting protocol that elects one node master; each remaining node is a secondary. The master is responsible for synchronizing information across the cluster. When quorum is formed, it is maintained by continual voting; if the master goes offline, a new master is elected by the nodes that remain online. Quorum must be maintained for the cluster to function fully. Because there is the possibility of a tie in a cluster that has an even number of nodes, one node can be configured to hold epsilon, which is an extra fractional voting weight. For instance, in a four-node cluster, quorum can be maintained if two nodes cast the same vote and one of those nodes holds epsilon. The system administrator can set epsilon on one node at most. Epsilon can be unassigned and reassigned as needed.

If you have a two-node cluster, you must configure cluster high availability (HA). For more information, see the Data ONTAP Cluster-Mode High Availability Configuration Guide.

The nodes in a cluster communicate over a dedicated, physically secure Ethernet network. The cluster logical interfaces (LIFs) on each node in the cluster must be on the same subnet. For information about network management for cluster and nodes, see the Data ONTAP Cluster-Mode Network Management Guide.

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What a node in the cluster is

A node is a controller that runs the Data ONTAP Cluster-Mode software. In a cluster, it is connected to other nodes over a cluster network.

Storage units for managing disk space

To properly provision storage, it is important to define and distinguish between the different units of storage.

Where to find additional Cluster-Mode information

System Manager Help provides basic Data ONTAP operating in Cluster-Mode conceptual information that is relevant to the tasks that you can perform using System Manager. For in-depth conceptual information that you might require for configuration, monitoring, and management of storage objects and storage systems, you can see the Data ONTAP documentation available on the NetApp Support Site.

Dashboard window

The dashboard contains multiple panels that provide cumulative at-a-glance information about your system and its performance. You can use the Dashboard window to view various aspects of your storage management environment, such as space and CPU utilization, the status of storage objects, notifications, system properties, network throughput, and protocol operations.

Viewing storage system details

You can use the Home tab to view the details of a storage system, such as the name, IP address, status of a storage system, and version of Data ONTAP that the storage system is running.