While analyzing the storage I/O profile of a file-server workload, you notice that each magnetic hard drive in the array reports an average rotational latency of about 4.2 ms. Based on standard spindle speeds for enterprise HDDs, which rotational speed is the array most likely using?
15 000 RPM → 0.5 × (60 000 ÷ 15 000) = 2 ms The observed 4.2 ms latency aligns most closely with the theoretical 4.17 ms value, indicating 7 200-RPM disks. Lower-speed 5 400-RPM drives would be noticeably slower (~5.6 ms), while 10 000- and 15 000-RPM drives would show faster latencies of ~3 ms and ~2 ms respectively.