--- title: "Requirements of a DFS" subject: "Distributed System" chapter: 2 key: "semester_7/distributed_system:dfs-requirements" source: https://www.bctengineer.com/q/semester_7/distributed_system/dfs-requirements site: BCT Engineering --- # Requirements of a DFS Distributed System · Chapter 2: Distributed Objects and File System - Asked in: Model question - Video: [INTRODUCTION TO DISTRIBUTED FILE SYSTEM (DFS)](https://www.youtube.com/watch?v=hkgpkQZI1oU) — Taha Mohamed - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/distributed_system/dfs-requirements - Whole chapter: https://www.bctengineer.com/md/semester_7/distributed_system/chapter-2 ## Question Define distributed file system (DFS). What are the different requirements of the distributed file system? ## Short answer A DFS allows network-wide file access with a single namespace. Requirements include transparency, concurrent update control, replication, heterogeneity, fault tolerance, consistency, security, and efficiency comparable to local file systems. ## Answer #### Distributed file system A **distributed file system (DFS)** allows files stored at several servers to be accessed and shared by clients over a network as if they were on a local disk. It gives one name space and hides the distribution. #### Requirements 1. **Transparency:** access, location, mobility, performance and scaling transparency, so users see one file tree. 2. **Concurrent file updates:** changes by one client must not disturb others; locking or optimistic control is needed. 3. **File replication:** copies of a file at several servers share load and improve fault tolerance. 4. **Hardware and operating system heterogeneity:** interfaces must be defined so clients and servers run on any OS or hardware. 5. **Fault tolerance:** service continues after client or server crashes (idempotent, stateless operations, retransmission). 6. **Consistency:** the system should provide, or closely approximate, one-copy update semantics, as in a local file system. 7. **Security:** authentication and access control lists on requests, with encryption when needed. 8. **Efficiency:** performance comparable to a local file system, using caching, read-ahead and delayed write. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is a DFS transparency requirement? A. Clients must use different commands for remote files B. Files are visible only on one workstation C. Users must know the server of each file D. Users see one file tree regardless of where files are stored (access, location, mobility, performance, scaling) Answer: D. Transparency makes the distributed files look like a single local tree. (Key point: Transparency) 2. Why does a DFS need concurrency control? A. Because files are read-only B. To avoid replication C. Changes by one client must not disturb others, using locking or optimistic control D. To convert data formats Answer: C. Concurrent updates need locking or optimistic mechanisms. (Key point: Concurrent updates) 3. How does a DFS support fault tolerance? A. By forbidding retransmission B. Service continues after crashes through idempotent, stateless operations and retransmission C. By requiring all servers to be up D. By keeping one single copy of each file Answer: B. Idempotent stateless operations let clients retry safely. (Key point: Fault tolerance) 4. What is the benefit of file replication? A. Share load and improve fault tolerance B. It removes the need for caching C. It reduces number of servers needed D. It guarantees strict consistency automatically Answer: A. Copies at several servers distribute load and survive failures. (Key point: Replication) ## Related in Distributed System - [DFS requirements and file service architecture](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Adfs-requirements-architecture) — Distributed System, chapter 2 - [DFS architecture and storage sharing](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Adfs-architecture-sharing) — Distributed System, chapter 2, asked 4× - [Importance of DFS; operations of SUNNFS](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Adfs-importance-sunnfs) — Distributed System, chapter 2 - [Autonomous vs distributed system](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Aautonomous-vs-distributed) — Distributed System, chapter 1 - [Models of distributed system](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Amodels-of-ds) — Distributed System, chapter 1 - [True distributed system; middleware organisation](https://www.bctengineer.com/question.md?key=semester_7%2Fdistributed_system%3Atrue-ds-middleware) — Distributed System, chapter 3 ## 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 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