01. [10p] Rotational delay - IOPS calculations

Every disk in your storage system has a maximum theoretical IOPS value that is based on a formula. Disk performance and IOPS is based on three key factors:

  • Rotational speed. Measured in RPM, mostly 7,200, 10,000 or 15,000 RPM. A higher rotational speed is associated with a higher-performing disk.
  • Average latency. The time it takes for the sector of the disk being accessed to rotate into position under a read/write head.
  • Average seek time. The time (in ms) it takes for the hard drive’s read/write head to position itself over the track being read or written.
  • Average IOPS: Divide 1 by the sum of the average latency in ms and the average seek time in ms (1 / (average latency in ms + average seek time in ms).

To calculate the IOPS range divide 1 by the sum of the average latency in ms and the average seek time in ms. The formula is:

average IOPS = 1 / (average latency in ms + average seek time in ms).

Let's calculate the Rotational Delay - RD for a 10K RPM drive:

  • Divide 10000 RPM by 60 seconds: 10000/60 = 166 RPS
  • Convert 1 of 166 to decimal: 1/166 = 0.006 seconds per Rotation
  • Multiply the seconds per rotation by 1000 milliseconds (6 MS per rotation).
  • Divide the total in half (RD is considered half a revolution around a disk): 6/2 = 3 MS
  • Add an average of 3 MS for seek time: 3 MS + 3 MS = 6 MS
  • Add 2 MS for latency (internal transfer): 6 MS + 2 MS = 8 MS
  • Divide 1000 MS by 8 MS per I/O: 1000/8 = 125 IOPS

[10p] Task A - Calculate rotational delay

Add in your archive the operations and the result you obtained. (Screenshot, picture of calculations made by hand on paper)

Calculate the Rotational Delay, and then the IOPS for a 5400 RPM drive.

ep/labs/03/contents/tasks/ex1.txt · Last modified: 2021/10/26 10:46 by radu.mantu
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