NetApp Clustered Data ONTAP is an enterprise-ready, unified scale-out storage which increases the scalability, protocol support, and data protection capabilities. Scale-out storage is the most powerful and flexible way to respond to the inevitable data growth and data management challenges in today’s environments. With scale-out, as the storage environment grows, additional controllers are added seamlessly to the resource pool residing on a shared storage infrastructure. Scale-out, together with built-in storage virtualization, provides nondisruptive movement of host and client connections, as well as the datastores themselves, anywhere in the resource pool. With these capabilities, new workloads can be easily deployed and existing workloads can be easily and nondisruptively balanced over the available resources. Technology refreshes (replacing disk shelves, adding or completely replacing storage controllers) are accomplished while the environment remains online and serving data.

A clustered Data ONTAP system consists of NetApp storage controllers (including V-Series or FlexArray licensed systems) with attached disks. The basic building block is the high-availability (HA) pair which consists of two identical nodes, or instances of clustered Data ONTAP. Each node actively provides data services and has redundant cabled paths to the other node’s disk storage. If either node is down for any reason, planned or unplanned, its HA partner can take over its storage and maintain access to the data. When the downed system rejoins the cluster, the partner node gives back the storage resources. The storage nodes are combined into a cluster to form a shared pool of physical resources that are available to applications, SAN hosts, and NAS clients (see Figure 1). The shared pool appears as a single system image for management purposes, providing a single common point of management, through GUI or CLI tools, for the entire cluster.


Figure 1 : The NetApp Cluster architectural overview

A NetApp Cluster is composed of physical hardware such as storage controllers with attached disk shelves, network interface cards, and, optionally, Flash Cache cards. Together these components create a physical resource pool that is virtualized as logical cluster resources to provide data access. Abstracting and virtualizing physical assets into logical resources provide the flexibility and potential multi-tenancy in clustered Data ONTAP as well as the object mobility capabilities that are the heart of nondisruptive operations.

To understand the architecture of the NetApp Cluster in a better way, the components of the cluster are classified further into Physical Cluster Components and Logical Cluster Components. Let us now discuss each of them in detail.

Physical Cluster Components: Storage controllers, independent of the model, are considered equivalent in the cluster configuration in that they are all presented and managed as cluster nodes. Clustered Data ONTAP is a symmetrical architecture, with all nodes performing the same data-serving function.

Individual disks are managed by defining them into aggregates: groups of disks of a particular type that are protected by using NetApp RAID-DP technology, similar to 7-Mode.

Network interface cards and HBAs provide physical ports (Ethernet and Fibre Channel) for connection to the management and data networks.

The physical components provide a pool of shared resources from which the logical cluster resources are constructed. Applications and hosts access data only through storage virtual machines (SVMs) that contain volumes and logical interfaces.

Logical Cluster Components: The primary logical cluster component is the storage virtual machine (SVM); all client and host data access is via an SVM. Clustered Data ONTAP supports a minimum of one and up to hundreds of SVMs in a single cluster. Each SVM is configured for the client and host access protocols it supports—any combination of SAN and NAS. Each SVM contains at least one volume and at least one logical interface. The accessing hosts and clients connect to the SVM via a logical interface (LIF).

Owing to their high availability and efficient load distribution features, the NetApp Cluster is very popular in large, mission-critical IT infrastructures, which require ready and reliable storage services. In such environments, the non-availability of the storage system or any of its core components, rapid erosion of storage space provided by the storage system, and inconsistencies in I/O load-balancing across disks/LUNs/Aggregate/Volumes can result in short/prolonged delays in the delivery of storage services, which will ultimately slowdown the dependent end-user services. To avoid this, it is imperative to watch out for issues in the operations and usage of the cluster on a regular basis.