For random access to mechanical disks, the most significant impact on the time it takes to complete an IO is:

The total time to complete an I/O operation on a mechanical hard disk drive (HDD) is the sum of seek time, rotational latency, and data transfer time. For random access patterns, the read/write head must physically move across the disk platters to locate the correct track. This mechanical movement, known as seeking, is the most time-consuming part of the operation. Compared to the electronic speed of data transfer and the relatively predictable rotational delay, the physical seek time introduces the most significant latency, making it the primary bottleneck for random I/O performance on HDDs.

B. Rotation delay: While a significant component of latency, the time for the platter to spin to the correct sector is typically less than the average time required to move the head across random tracks.
C. Data transfer time: For the small block sizes typical of random I/O, the actual time spent transferring data is negligible compared to the mechanical delays of seeking and rotation.

1. Huawei HCIA-Storage V5.0 Training Material: In the chapter on "Storage Technology and Application

" the section on "HDD Technologies" explains that I/O response time is composed of seek time

rotational latency

and data transfer time. It explicitly identifies that for random

small I/O

the seek time is the most significant performance bottleneck. (Refer to: HCIA-Storage V5.0 Training Material

Chapter 2

Section: HDD Technologies).

2. Patterson

D. A.

& Hennessy

J. L. (2013). Computer Organization and Design: The Hardware/Software Interface (5th ed.). Morgan Kaufmann. In Chapter 6

"Storage and Other I/O Topics

" Section 6.1 provides an example calculation for disk access time. The example demonstrates that the average seek time (e.g.

8 ms) is the largest component

compared to average rotational latency (e.g.

4.17 ms for a 7200-RPM disk) and transfer time (e.g.

0.04 ms for a 4 KiB sector)

thus dominating the total access time for random requests.

3. Silberschatz

A.

Galvin

P. B.

& Gagne

G. (2018). Operating System Concepts (10th ed.). Wiley. Chapter 10

"Mass-Storage Structure

" Section 10.2.1

"Disk Structure

" details the components of disk access time. The text explains

"seek time... is the time for the disk arm to move the heads to the cylinder containing the desired sector." The subsequent discussion on disk scheduling algorithms (Section 10.2.2) is entirely focused on minimizing seek time

reinforcing its status as the dominant factor in disk latency.