F2FS – flash file system

F2FS (Flash-Friendly File System) is a flash file system initially developed by Samsung Electronics for the Linux kernel. It’s a good choice when installing Linux to an eMMC, SSD, NVMe, SDCard, or a flash-based USB device.

F2FS was designed on a basis of a log-structured file system approach, which it adapted to newer forms of storage. It aims to remedy some known issues of the older log-structured file systems, such as the snowball effect of wandering trees and high cleaning overhead.

In addition, since a NAND-based storage device shows different characteristics according to its internal geometry or flash memory management scheme (such as the Flash Translation Layer or FTL), it supports various parameters not only for configuring on-disk layout, but also for selecting allocation and cleaning algorithms.

Features include:

  • Multi-head logging.
  • Multi-level hash table for directory entries.
  • Static/Dynamic hot and cold data separation.
  • Adaptive logging scheme.
  • Configurable operational units.
  • Dual checkpoint.
  • Roll-back and roll-forward recovery.
  • Heap-style block allocation
  • TRIM/FITRIM support.
  • Online fs defragmentation/file defragmentation.
  • Inline xattrs.
  • Inline data.
  • Inline dir.
  • Offline filesystem check (Check and fix inconsistency).
  • Atomic operations – very limited functionality for atomic write support.
  • Filesystem-level encryption.
  • Offline resizing – expand existing partition with resize.f2fs.
  • Inner periodically data flush – try to flush user data before starting a checkpoint. So user’s data written after last checkpoint which may not be fsynced could be saved
  • Extent cache – rb-tree based extent cache.
  • Move_file_range – moving a range of data blocks from source file to destination file.
  • Host-managed SMR.
  • Multiple devices support – shows them entirely as one big volume under one f2fs instance.
  • Large IO submission – IO alignment by filling dummy blocks in DATA and NODE write bio.
  • Disk Quota (user/group).
  • Cleaning both on demand and in the background. On-demand cleaning is triggered when there are not enough free segments to serve VFS calls. Background cleaner is operated by a kernel thread, and triggers the cleaning job when the system is idle.
  • Cleaning Overhead:
    • Support a background cleaning process.
    • Support greedy and cost-benefit algorithms for victim selection policies.
    • Support multi-head logs for static/dynamic hot and cold data separation.
    • Introduce adaptive logging for efficient block allocation.

Website: f2fs.wiki.kernel.org
Developer: Samsung Electronics, Motorola Mobility, Huawei and Google
License: GNU General Public License version 2 only

F2FS is written in C. Learn C with our recommended free books and free tutorials.

Return to Journaling File Systems Home Page

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