What a cluster is

You can group pairs of nodes together to form a scalable cluster. Creating a cluster enables the 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.

A cluster can contain up to 24 nodes (or up to 10 nodes if it contains a Vserver with an Infinite Volume). Each node in the cluster can view and manage 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, spans 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 High Availability Configuration Guide for Cluster-Mode.

The nodes in a cluster communicate over a dedicated, physically isolated and 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 Network Management Guide for Cluster-Mode.

For information about setting up a cluster or joining a node to the cluster, see the Data ONTAP Software Setup Guide for Cluster-Mode.

Next Topic

What a node in the cluster is

A node is a controller in a cluster. It is connected to other nodes in the cluster over a cluster network. It is also connected to the disk shelves that provide physical storage for the Data ONTAP system or to third-party storage arrays that provide array LUNs for Data ONTAP use.

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 to help you perform tasks using System Manager. For in-depth conceptual information to help you configure, monitor, and manage 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 information about 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.

Storage window

You can click the links to manage the resources of your cluster or node.

Configuration window

The Configuration window provides links to the following: Security, system tools, Snapshot policies, schedules, and peers.

Security window

The Security window provides links to the following: Users and roles.

Services window

The Services window provides links to the following: LDAP and Kerberos.

System Tools window

The System Tools window provides links to the following: DateTime, Licenses, and SNMP.

Diagnostics window

The Diagnostics window provides links to the following: Job, system health, Flash Pool statistics, and logs.

Logs window

The Logs window provides links to the following: Events and SnapMirror log.