Which of the following is NOT a benchmark test performed in Linux?

The correct choice is iPerf, as it serves a different purpose compared to the other options listed. iPerf is primarily designed for measuring and analyzing network performance, focusing on parameters like bandwidth, latency, and jitter for TCP and UDP connections. It is widely used to test the speed and performance of network connections rather than disk I/O performance.

In contrast, the other tools mentioned are specifically aimed at assessing storage performance. IOR is used for evaluating file system performance by measuring I/O throughput for large files across different file systems. fio is a flexible I/O tester and benchmark that can simulate various workloads to evaluate different aspects of storage performance, including random and sequential access patterns. IO500 is a benchmark suite that focuses on evaluating the performance of file systems and storage systems, particularly in high-performance computing (HPC) environments.

Thus, iPerf being network-focused distinguishes it from the disk-oriented benchmarks of the other options.