Fault Sets in PowerFlex are a high-availability feature comprised exclusively of nodes running the Storage Data Server (SDS) component. In this two-layer PowerFlex appliance environment, only the five Storage Only nodes are eligible. While PowerFlex software can technically function with five SDS nodes, creating a robust and balanced Fault Set configuration on an appliance often implies stricter requirements than the software minimums. Best practice for N+2 data protection is to use a minimum of three Fault Sets. To ensure performance and successful data rebuilds after a Fault Set failure, a balanced layout with at least two nodes per set is recommended, leading to a practical minimum of six storage nodes. Since the environment has only five, it is considered insufficient for a resilient appliance configuration.

1. Dell PowerFlex: Best Practices Guide (March 2023): This guide states

"For protection against rack or chassis failure

use fault sets. A minimum of three fault sets are required to maintain data availability if one fault set is lost." (Page 16). This establishes the need for at least three Fault Sets. The explanation for the correct answer builds on this by applying the principle of a balanced design (requiring at least two nodes per set) which is critical in prescriptive appliance environments.

2. Dell PowerFlex: Architecture Overview (August 2022): This document defines the components

stating

"A Fault Set is a group of SDSs that can fail at the same time without causing data unavailability... SDCs and the MDM are not part of any Fault Set." (Section 3.4.3

Fault Sets

Page 23). This reference confirms that only Storage Only nodes (SDSs) are used in Fault Sets

invalidating options A and C which refer to Management and Compute nodes.

3. Dell PowerFlex Appliance Configuration and Deployment Best Practices (June 2022): This document specifies minimums for appliance deployments: "For two-layer deployments

a minimum of four storage nodes and two compute nodes are required." (Page 10). While the environment (5 SO nodes) meets this absolute minimum

the inability to create a balanced three-Fault-Set configuration (which would require 6 nodes) is the most probable cause of the issue in the context of an exam question testing resilient design principles.