Before beginning hardware planning, decide if the higher availability obtained by clustering two N series storage system nodes is needed. These higher availability configurations are referred to as HA (high availability) pairs in Data ONTAP 8.x, as active/active configurations in Data ONTAP 7.2 and 7.3, and as clustered configurations in Data ONTAP 7.1.
An HA pair (or active/active configuration) consists of two storage systems (nodes) whose controllers are connected to each other either directly or, in the case of a fabric-attached MetroCluster, through switches and FC-VI interconnect adapters. You can configure the HA pair so that each node in the pair shares access to a common set of storage, subnets, and tape drives, or each node can own its own distinct set of storage. The nodes are connected to each other through a NVRAM adapter, or, in the case of systems with two controllers in a single chassis, through an internal interconnect. This allows one node to serve data that resides on the disks of its failed partner node. Each node continually monitors its partner, mirroring the data for each other’s nonvolatile memory (NVRAM or NVMEM).
Two N series storage system nodes can be clustered together for higher availability using the Cluster Failover (CFO) software feature.
IBM® N3150 consists of single-node (A15) and dual-node (A25) (active-active) base units.
IBM N3220 (A12 and A22) and N3240 (A14 and A24) have two models each. N3220 and N3240 are available in a single enclosure system where models A12 and A14 are available as a single node and models A22 and A24 are available as dual node.
Active/active or high availability configuration IBM N3300, N3400, N3600 and N6000 series systems all contain both clustered (active/active or high availability) nodes in the same enclosure.
IBM N6200 series HA models that do not include Input/Output expansion modules contain both nodes in the same enclosure. Dual-controller IBM N6200 series models that do include Input/Output expansion modules contain controller nodes in separate enclosures.
IBM N7x50T series includes N7950T Model E22 that is a dual node, dual enclosure system. It has one controller module and one Input/Output expansion module in each enclosure. N7550T is an active/active dual-node base unit.
Configuring storage systems in an HA pair (or active/active configuration) provides the following benefits:
When one node fails or becomes impaired, a takeover occurs, and the partner node continues to serve the failed node’s data.
When you halt one node and allow takeover, the partner node continues to serve data for the halted node while you upgrade the node you halted. For more information about nondisruptive upgrades, see the Data ONTAP Upgrade Guide or Upgrade and Revert/Downgrade Guide for your version of Data ONTAP.
When you halt one node and allow takeover, the partner node continues to serve data for the halted node while you replace or repair hardware in the node you halted.