You are upgrading an iSCSI SAN that will host a latency-sensitive OLTP database. The design document specifies that the average rotational latency of every magnetic disk must not exceed 2 milliseconds. Which hard-disk spindle speed should you choose to satisfy this requirement?
Average rotational latency is one-half of the time it takes a platter to complete one full revolution (60 s ÷ RPM ÷ 2). - 5 400 RPM: 60/5 400 ≈ 11.1 ms per revolution → ≈ 5.6 ms average latency. - 7 200 RPM: 60/7 200 ≈ 8.3 ms per revolution → ≈ 4.2 ms average latency. - 10 000 RPM: 60/10 000 ≈ 6 ms per revolution → ≈ 3 ms average latency. - 15 000 RPM: 60/15 000 ≈ 4 ms per revolution → ≈ 2 ms average latency. Only 15 000-RPM drives achieve an average rotational delay of about 2 ms, meeting the stated requirement; the other spindle speeds leave latency above the 2-ms threshold.
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Why is average rotational latency calculated as half the time of one full revolution?
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What makes higher RPM drives, like 15,000 RPM, suitable for latency-sensitive workloads?
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