Filesystems

A filesystem is the layer that organizes how data is stored on a storage device and how it is accessed by the operating system and applications. It provides a persistent namespace of files and directories, enforces access permissions, and manages metadata and allocation of space. The filesystem presents a conventional file hierarchy to users and is mounted at a particular path or network share.

Data on a filesystem is stored in blocks or extents and described by metadata. Inodes or directory entries link filenames to their metadata and data blocks. Journaling or copy-on-write mechanisms track changes to improve reliability in the event of crashes. Fragmentation, metadata overhead, and allocation strategies influence performance and capacity planning.

Common families include Linux file systems such as ext4, XFS, and Btrfs; Windows file systems such as NTFS and ReFS; and macOS file systems such as APFS and HFS+. Simple or portable formats include FAT32 and exFAT. Networked filesystems like NFS and SMB provide access to remote storage through conventional file semantics.

Key features vary by system and may include journaling, copy-on-write, snapshots, compression, encryption at rest, quotas, ACLs, and extended attributes. Permissions and links (hard and symbolic) control access and structure. Some systems support advanced data integrity measures such as checksums and RAID-aware metadata.

Choosing a filesystem involves trade-offs among reliability, performance, scalability, and compatibility with operating systems and workloads. Consider maximum file size and volume size, latency, write patterns, and backup strategies. The ecosystem evolves, with ongoing work in scalable metadata, deduplication, and seamless integration with cloud and network storage.