JFFS

The Journaling Flash File System (or JFFS) is a log-structured file system for use on NOR flash memory devices on the Linux operating system. It has been superseded by JFFS2.

Design

Flash memory (specifically NOR flash) must be erased prior to writing. The erase process has several limitations:

These constraints combine to produce a profound asymmetry between patterns of read and write access to flash memory. In contrast, magnetic hard disk drives offer nearly symmetrical read and write access: read speed and write speed are nearly identical (as both are constrained by the rate at which the disk spins), it is possible to both read and write small blocks or sectors (typically 512 or 4096 bytes), and there is no practical limit to the number of times magnetic media can be written and rewritten.

JFFS2

Journalling Flash File System version 2 or JFFS2 is a log-structured file system for use with flash memory devices. It is the successor to JFFS. JFFS2 has been included into the Linux kernel since September 23, 2001, when it was merged into the Linux kernel mainline as part of the kernel version 2.4.10 release. JFFS2 is also available for a few bootloaders, like Das U-Boot, Open Firmware, the eCos RTOS and the RedBoot. Most prominent usage of the JFFS2 comes from OpenWrt.

At least three file systems have been developed as JFFS2 replacements: LogFS, UBIFS, and YAFFS.

Features

JFFS2 introduced: