N-Step-SCAN disk scheduling
Last Updated : 29 Aug, 2023
The input-output requests that are coming from the disk are scheduled by the operating system and that scheduling of the disk is known as disk scheduling. Disk scheduling is important since multiple requests come from processes for disk but only one disk is assigned to process at a time. Seek time is one of the crucial parameters in the operating system. Requests are linked in queues henceforth seek time gets increased due to which the system becomes slow. The algorithm which is used for disk scheduling is known as Disk Scheduling Algorithm whose purpose is to reduce total seek time.
N-Step-SCAN also called N-Step-Look is actually a Disk Scheduling Algorithm. It helps in determining the motion of the Disk's arm and also helps in servicing read and write requests. It divides the request queue into sub queues of length N. By doing this it ensures that the service guarantee objective is achieved. After this subsequent request is done they can not be allocated into N-size sub-queues since they are full by the elevator algorithm. Therefore starvation is completely eliminated and the service within N requests is guaranteed.
The N-Step-SCAN disk scheduling algorithm is a variation of the SCAN disk scheduling algorithm. Like SCAN, it works by scanning the disk surface in one direction and servicing requests along the way. However, instead of reversing direction at the end of the disk and servicing requests in the opposite direction, N-Step-SCAN divides the disk into N zones and scans each zone separately before moving on to the next zone.
By dividing the disk into zones and scanning each zone separately, N-Step-SCAN can improve disk scheduling performance by reducing the amount of time required to change the scanning direction. This can be particularly beneficial in systems with high disk I/O loads.
Overall, N-Step-SCAN is a useful disk scheduling algorithm that can improve performance in certain circumstances, particularly in systems with high disk I/O loads. However, it requires careful tuning to achieve optimal performance and may not be the best choice for all systems.
Algorithm for N-Step-SCAN Disk Scheduling
Step 1: A buffer is created for N requests.
Step 2: All the requests that are kept in this buffer are serviced in any specific wipe.
Step 3: During this time all the new incoming requests can not be added to this buffer, these new requests will be kept in a separate buffer.
Step 4: Now here comes the role of the I/O (Input Output) scheduler because when these top N requests are serviced, I/O (Input Output) scheduler chooses the next N requests and this process goes on and on.
Step 5: By doing this N-Step-SCAN allows better throughput and it is devoid of thrust.
Advantages of the N-Step-SCAN Disk Scheduling Algorithm
- Reduces Head Movement: By dividing the disk into zones and scanning each zone separately, N-Step-SCAN can reduce the amount of head movement required to service requests, which can improve overall disk I/O performance.
- Improves Throughput: By reducing head movement and improving disk I/O performance, N-Step-SCAN can improve overall system throughput, particularly in systems with high disk I/O loads.
- Allows for Fine-Tuning: The zone size in N-Step-SCAN can be adjusted to balance the competing goals of reducing head movement and ensuring a reasonably uniform distribution of requests across zones, allowing for fine-tuning to achieve optimal performance.
Disadvantages of the N-Step-SCAN Disk Scheduling Algorithm
- Complexity: N-Step-SCAN is more complex than some other disk scheduling algorithms, which can make it more difficult to implement and maintain.
- Requires Careful Tuning: The zone size in N-Step-SCAN must be carefully chosen to achieve optimal performance, which can require additional effort and expertise.
- May not be optimal for all systems: The benefits of N-Step-SCAN may not be realized in all systems, particularly those with low disk I/O loads or very large disk sizes.
- Overall, N-Step-SCAN is a useful disk scheduling algorithm that can improve performance in certain circumstances, particularly in systems with high disk I/O loads. However, it requires careful tuning and may not be the best choice for all systems.
Important Points to Keep in Mind About the N-Step-SCAN Disk Scheduling Algorithm
- The N-Step-SCAN algorithm is a variation of the SCAN algorithm that divides the disk into N sections and services requests in each section before moving on to the next section.
- The value of N can be adjusted to suit different disk configurations and workload patterns.
- N-Step-SCAN may not be optimal in situations with a large amount of data to be read or written in one direction, as it may lead to a large
- number of requests being queued up in the opposite direction.
- The algorithm may not be suitable for real-time systems where fast response times are critical.
- N-Step-SCAN is relatively simple to implement and does not require a large amount of memory or processing power.
Similar Reads
SCAN - EDF Scheduling in OS SCAN-EDF is a disk scheduling algorithm that is the same as the EDF algorithm but utilizes the seek optimization technique of the 'SCAN' algorithm when similar deadlines occur. It is a hybrid algorithm. To understand the importance of this algorithm, let us first look at the drawbacks of strictly fo
4 min read
FScan disk scheduling algorithm Fixed period SCAN (FSCAN) disk scheduling algorithm mainly focuses on handling high variance in shortest seek time first (SSTF). SCAN algorithm is also proposed to handle above mentioned situation but using SCAN algorithm causes long delay while handling requests which are at extremes of disk. FSCAN
3 min read
C-SCAN Disk Scheduling Algorithm Given an array of disk track numbers and initial head position, our task is to find the total number of seek operations to access all the requested tracks if a C-SCAN Disk Scheduling algorithm is used.The Circular SCAN (C-SCAN) Scheduling Algorithm is a modified version of the SCAN Disk Scheduling A
12 min read
I/O scheduling in Operating Systems Input/Output (I/O) operations are how a computer communicates with external devices such as hard drives, keyboards, printers, and network interfaces. These operations involve transferring data into and out of the system whether it’s reading a file, saving a document, printing, or sending data over a
6 min read
SCAN (Elevator) Disk Scheduling Algorithms In the SCAN Disk Scheduling Algorithm, the head starts from one end of the disk and moves towards the other end, servicing requests in between one by one and reaching the other end. Then the direction of the head is reversed and the process continues as the head continuously scans back and forth to
12 min read