In a multi-node Dell Avamar grid, a spare node provides high availability and fault tolerance through a technology called RAIN (Redundant Array of Independent Nodes). The spare node remains in a standby state during normal operation. If an active data node in the grid experiences a hardware failure, the Avamar system automatically fails over to the spare node. The spare node is activated and integrated into the grid, and the data from the failed node is rebuilt onto it using the parity information distributed across the remaining data nodes. This ensures the grid remains operational and protected while the failed hardware is replaced.

A. The utility node has dedicated management functions and is not load-balanced by a spare node.

B. Capacity is grown by adding new data nodes to the grid, not by activating a standby spare node.

D. An NDMP accelerator is a specialized node type for backing up NAS devices and is distinct from a general-purpose spare node.

1. Dell Avamar 19.9 Administration Guide, Page 26, "RAIN". The guide explicitly states, "If a data node fails, a spare node, if configured, automatically replaces the failed node. The system rebuilds the data from the failed node on the spare node by using the RAIN parity information."

2. Dell Avamar Server and Data Store Hardware Information Guide, "Node types" section. This document describes the roles of different nodes, defining the spare node's purpose as a standby component for RAIN protection to replace a failed data node.