Disk Scheduling & Management

Disk Management

Definition

• Disk management refers to the process of organizing, partitioning, formatting, and managing storage devices such as hard drives, solid-state drives (SSDs), and other storage media. 

Characteristics

• Different operating systems provide various in-built tools and utilities for disk management which are briefly discussed below –

  • Windows:

    • Windows operating systems, such as Windows 10 and Windows Server, offer a built-in disk management tool called “Disk Management.” This tool allows one to perform tasks like creating and formatting partitions, extending or shrinking volumes, assigning drive letters, and converting disks between different formats (e.g., Basic and Dynamic disks). We can use the Disk Management tool by right-clicking on the “Start” button and selecting “Disk Management” or by searching for “Disk Management” in the Start menu and following the steps one by one.

  • Mac OS:

    • Mac OS provides a disk utility tool called “Disk Utility” for managing disks and partitions. We can use it to format, partition, repair, and encrypt disks. To use this Disk Utility on MacOS, go to “Applications” > “Utilities” > “Disk Utility.”

  • Linux:

    • Linux distributions typically include various disk management tools, depending on the desktop environment or distribution. Some popular disk management tools for Linux are:-

      1. GParted: A powerful graphical partition editor that allows you to create, resize, move, and delete partitions.
      2. fdisk: A command-line tool for creating and managing partitions.
      3. parted: A command-line partitioning utility with more advanced features than fdisk.

  • Unix and BSD:

    • Unix and BSD operating systems provide tools like fdisk and gpart for disk partitioning and management. These command-line tools are similar to their Linux counterparts.

  • Chrome OS:

    • Chrome OS is a lightweight operating system primarily designed for web-based applications and Chromebooks.
    • Disk management on Chrome OS is relatively limited compared to other operating systems.
    • Users can manage external storage devices such as USB drives or SD cards by accessing the “Files” app, where they can format and manage the connected storage devices.
• There are several third-party disk management tools are also available for various operating systems to manage disks.

Disk Scheduling

• Disk scheduling is a key component of the operating system that determines the order in which pending input/output (I/O) requests are serviced by the disk.
• The disk scheduling algorithm aims to optimize disk utilization, reduce seek time, and improve overall system performance.
• There are several types of disk scheduling algorithms and each disk scheduling algorithm has its own advantages and trade-offs, and the choice of algorithm depends on the specific system requirements and workload characteristics.
• Each disk scheduling algorithm has its advantages and trade-offs in terms of performance metrics like average seek time, throughput, fairness, and starvation prevention. The choice of the appropriate disk scheduling algorithm depends on the specific characteristics of the workload and system requirements.
• Some commonly used disk scheduling algorithms are:-

• • First-Come, First-Served (FCFS) Disk Scheduling:

    • This is the simplest disk scheduling algorithm where I/O requests are serviced in the order they arrive.
    • In this, the disk arm moves to the requested track and fulfills the request.
    • FCFS is easy to implement but can lead to poor performance when there are large variations in seek times.

  • Shortest Seek Time First (SSTF) Disk Scheduling:

    • SSTF selects the I/O request with the shortest seek time from the current position of the disk arm.
    • This algorithm minimizes arm movement, resulting in reduced seek times.
    • SSTF tends to provide better performance than FCFS but may cause starvation for requests located farther from the current position.

  • SCAN (Elevator) Disk Scheduling:

    • In the SCAN algorithm, also known as the elevator algorithm, the disk arm starts at one end of the disk and moves in a single direction, serving all requests in that direction until it reaches the end. Then it reverses direction and serves the remaining requests in the opposite direction.
    • This algorithm prevents starvation and provides a fair distribution of service. However, requests located in the opposite direction of the disk arm may experience longer wait times.

  • Circular SCAN (C-SCAN) Disk Scheduling:

    • C-SCAN is an improved version of the SCAN algorithm that guarantees a more uniform servicing of I/O requests. Instead of reversing direction at the end of the disk, the disk arm moves to the opposite end and starts again.
    • This ensures that all requests are serviced without any starvation, although it may lead to a longer total service time.

  • LOOK Disk Scheduling:

    • The LOOK algorithm is similar to SCAN but does not traverse the entire disk in both directions. Instead, it changes direction when there are no pending requests in the current direction.
    • This reduces the total seek time compared to SCAN but can still lead to uneven distribution of service and potential starvation.

  • Circular LOOK (C-LOOK) Disk Scheduling:

    • C-LOOK is an improvement over LOOK where the disk arm moves only to the last request in the current direction and then jumps to the first request in the opposite direction.
    • This avoids unnecessary traversals of empty disk areas and provides better performance than LOOK.
  • Other disk scheduling algorithms include Enhanced SCAN (ESCAN), Deadline-Based Scheduling, and N-step SCAN, among others.