--- title: "File system performance indicators" subject: "Operating System" chapter: 5 key: "semester_6/operating_system:fs-performance-indicators" source: https://www.bctengineer.com/q/semester_6/operating_system/fs-performance-indicators site: BCT Engineering --- # File system performance indicators Operating System · Chapter 5: File Systems - Asked in: 2073 Bhadra, 4 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/operating_system/fs-performance-indicators - Whole chapter: https://www.bctengineer.com/md/semester_6/operating_system/chapter-5 ## Question List the file system performance indicators with brief explanation. ## Short answer Throughput (data rate), response time/latency, disk access time (seek + rotation + transfer), cache hit ratio, disk space utilization, internal and external fragmentation, number of disk accesses per operation, reliability, and CPU overhead. ## Answer File system performance indicators are measures used to judge how well a file system works: 1. **Throughput (data rate):** amount of data transferred per second (KB/s or MB/s), depending on block size and the allocation scheme. 2. **Response time / latency:** time from issuing a request (open, read, write) to its completion. 3. **Disk access time:** seek time + rotational latency + transfer time; reduced by good layout (contiguous blocks), scheduling and caching. 4. **Cache (buffer) hit ratio:** fraction of requests served from the block cache without disk access; higher means better performance. 5. **Disk space utilization:** percentage of disk space used by useful data; affected by block size, fragmentation and metadata overhead. 6. **Fragmentation:** internal (unused part of last block) and external/file fragmentation, which increases seeks. 7. **Number of disk accesses per operation** (including directory lookup and i-node reads). 8. **Reliability and recoverability:** consistency after crash, and **scalability** to large disks and files. 9. **CPU overhead:** CPU time consumed by file system operations. Techniques to improve them: block caching, read-ahead, reducing arm motion (placing i-nodes in the middle of disk or in cylinder groups), defragmentation and a proper block size. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Disk access time is made up of: A. Seek time + rotational latency + transfer time B. Seek time + response time + hit ratio C. Throughput + latency + fragmentation D. Rotational latency + CPU overhead only Answer: A. Access time is the arm movement, wait for the sector, and data transfer. (Key point: Disk access time) 2. What does a high cache (buffer) hit ratio indicate? A. Many requests had to go to disk B. A large fraction of requests are served from the block cache without disk access, so performance is better C. The disk is highly fragmented D. Disk space utilization is low Answer: B. Hits avoid disk I/O entirely, so a higher ratio means better performance. (Key point: Cache hit ratio) 3. Throughput of a file system is: A. Time from issuing a request to its completion B. Percentage of disk used by useful data C. The amount of data transferred per second D. Time for the arm to reach a cylinder Answer: C. Throughput is the data rate (KB/s, MB/s); the time to completion is response time or latency. (Key point: Throughput) 4. Why is fragmentation a performance indicator? A. It reduces the number of disk accesses B. It raises the cache hit ratio C. It only affects CPU overhead D. File fragmentation increases seeks, and internal fragmentation wastes the unused part of the last block Answer: D. Scattered blocks need extra seeks and unused space in the last block lowers space utilization. (Key point: Fragmentation effect) ## Related in Operating System - [File attributes; FS implementation ways](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Afile-attribute-implementation-best) — Operating System, chapter 5 - [File system layout, i-node, backup](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Afs-layout-inode-backup) — Operating System, chapter 5 - [File system layout; i-node vs linked list](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Afs-layout-inode-vs-linked-list) — Operating System, chapter 5 - [Linked list file system; block size impact](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Afs-linked-list-block-size) — Operating System, chapter 5 - [File system layout; interface vs implementation](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Afs-layout-interface-vs-implementation) — Operating System, chapter 5 - [File system layout; free block management](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Afs-layout-free-blocks) — Operating System, chapter 5 ## Related in other subjects - [Google File System architecture](https://www.bctengineer.com/question.md?key=semester_8%2Fbig_data_technologies%3Agfs-architecture) — Big Data Technologies, chapter 2, asked 2× - [File system handling of kernel](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Akernel-file-system-handling) — Embedded System, chapter 6 - [File size: 60 s, 44.1 KHz, 8-bit stereo](https://www.bctengineer.com/question.md?key=semester_8%2Fmultimedia_system%3Aaudio-size-60s-44khz-8bit) — Multimedia System, chapter 2, asked 3× - [File size: 30 s, 44.1 KHz, 8-bit stereo](https://www.bctengineer.com/question.md?key=semester_8%2Fmultimedia_system%3Aaudio-size-30s-44khz-8bit) — Multimedia System, chapter 2, asked 3×