Filsystemdesign

Filsystemdesign, commonly written as file system design, refers to the set of principles, algorithms, and data structures used to store, organize, and retrieve information on storage devices. It defines how data is laid out on media, how metadata is maintained, and how the interface presented to applications behaves.

Key components include the block layout (block size, allocation unit), metadata management (inodes or file metadata tables), and the directory structure. Allocation strategies determine how files occupy space: contiguous allocation simplifies sequential access but is fragmentation-prone; linked or extent-based methods support dynamic growth and reduce fragmentation; modern designs often use extent trees or B-trees to index blocks efficiently.

Metadata and data structures affect performance and reliability. Inode-based file systems store metadata separately from data blocks; directory entries map names to inodes. Journaling and write-ahead logging provide crash consistency by recording changes before applying them. Copy-on-write designs, like some modern file systems, ensure on-disk consistency by never overwriting metadata in place.

Reliability and recovery also involve redundancy and checksums, such as RAID integration, data integrity checksums, and replication in distributed file systems. Permissions and access control (POSIX permissions, ACLs, extended attributes) govern how users and processes interact with files.

File system choices reflect trade-offs among performance, reliability, and scalability. Workloads with large files and sequential access may favor different layouts and caching strategies than metadata-heavy workloads with many small files. Local file systems differ from distributed or object-based approaches, which emphasize metadata distribution, fault tolerance, and scalability.