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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:
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:
- 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).
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
Calculate the rotational delay (RD) for a 5400 RPM drive.
