File Systems
File Systems
A file system is a vital component of an operating system that manages how data is stored and retrieved on a storage device. The concept of file systems has evolved significantly from its original use in organizing paper documents to becoming a sophisticated tool in modern computing.
Historical Context
Before the advent of computers, the term "file system" referred to methods of organizing, storing, and retrieving paper documents. By 1961, as computers began to rise in prominence, the term was repurposed to describe computerized methods of managing files and data storage.
Architecture of File Systems
A file system's architecture can be described in layers of abstraction, which, while conceptually separated, may not be distinctly partitioned in actual implementation. These layers include:
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Logical File System: This provides a high-level application programming interface (API) for file operations such as open, close, read, and write. It delegates operations to lower layers, allowing for abstraction from physical data storage concerns.
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Virtual File System (VFS): This optional layer supports multiple concurrent instances of physical file systems, each termed a file system implementation. It acts as an interface for kernel operations across different types of physical file systems.
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Physical File System: This layer provides relatively low-level access to a storage device like a hard disk drive or solid-state drive, managing the storage, retrieval, and updating of data.
Types of File Systems
File systems come in various types, each tailored to specific needs and environments:
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Journaling File System: This type logs changes before they are made, assisting in faster recovery after system crashes. Examples include ext3 and NTFS.
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Clustered File System: These allow multiple servers to simultaneously access a single storage system, enhancing performance and redundancy. Lustre is a popular example used in high-performance computing environments.
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Hierarchical File System: Organizes files in a tree structure, which is intuitive for users and efficient for certain file retrieval operations. An example is Apple's HFS+.
Implementation and Usage
File systems are implemented across various devices and operating environments. Local file systems are used directly on computers, while distributed file systems like Apache Hadoop are designed for scalability and are used in managing large-scale data across multiple machines.
Certain file systems, such as tmpfs, store files in virtual memory, providing faster access speeds but at the cost of volatility. Conversely, traditional file systems manage persistent storage.
File-System Permissions
File-system permissions are crucial for security. They control access to files and directories using models like the access-control list (ACL). POSIX standards define permissions based on older Unix-based models, ensuring compatibility and security across different systems.
Notable File Systems
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FAT (File Allocation Table): Widely used in older Windows systems and still prevalent in mobile devices and embedded systems due to its simplicity.
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Lustre File System: Known for its high performance, especially in large-scale computing environments.