What initiates an automatic NAS server failover to the peer SP?

An automatic NAS server failover is a high-availability (HA) function triggered by an unplanned, critical event. If the Storage Processor (SP) that owns a NAS Server experiences a catastrophic hardware fault (e.g., CPU, memory, or power failure) or becomes non-responsive, the system automatically initiates a failover. This process transfers the ownership and operational control of the NAS Server and its associated file systems to the peer SP. This ensures service continuity for connected clients with minimal interruption. This fault-driven, reactive process is distinct from planned administrative actions like migrations or resource balancing.

A. Assisted internal migration: This is a planned, administrator-initiated process for moving resources for maintenance or upgrades, not an automatic failover due to a fault.
B. Network link failure: Dell storage systems use technologies like Link Aggregation and Fail-Safe Networking to provide redundancy, handling individual link failures without requiring a full NAS server failover.
D. Resource balancing algorithm: This describes a proactive, non-disruptive process for optimizing performance across SPs, which is fundamentally different from a reactive failover caused by a hardware failure.

1. Dell EMC Unity: High Availability - A Detailed Review (White Paper), April 2022.

Page 13, Section "NAS Server High Availability": "If the SP that owns the NAS Server fails, the NAS Server automatically fails over to the peer SP. The peer SP takes ownership of the network interfaces and file systems of the failed NAS Server and continues to serve I/O to clients." This directly confirms that an SP failure (a hardware fault) triggers the automatic failover.

2. Dell EMC Unity XT: Unisphere Overview (White Paper), August 2022.

Page 10, Section "High availability": "The Unity XT family is designed for five 9s (99.999%) availability. This is achieved through redundant components such as dual Storage Processors (SPs) in an active/active configuration... In the event of an SP failure, the peer SP takes over and provides access to data." This reinforces that SP failure is the primary trigger for the HA takeover mechanism.