Moxa W325A-LX [7/74] Additional information about jffs2 is available at

W315A/325A Linux User's Manual Introduction

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Normally, the kernel uses the Root File System to boot up the system. The Root File System is protected, and

cannot be changed by the user. This type of setup creates a “safe” zone.

For more information about the memory map and programming, refer to Chapter 6, Programmer’s Guide.

Journaling Flash File System (JFFS2)

The Root File System and User Directory in the flash memory are formatted with the Journaling Flash File

System (JFFS2). The formatting process places a compressed file system in the flash memory. This operation

is transparent to the user.

The Journaling Flash File System (JFFS2), which was developed by Axis Communications in Sweden, puts a file

system directly on the flash, instead of emulating a block device. It is designed for use on flash-ROM chips and

recognizes the special write requirements of a flash-ROM chip. JFFS2 implements wear-leveling to extend the

life of the flash disk, and stores the flash directory structure in the RAM. A log-structured file system is

maintained at all times. The system is always consistent, even if it encounters crashes or improper

power-downs, and does not require fsck (file system check) on boot-up.

JFFS2 is the newest version of JFFS. It provides improved wear-leveling and garbage-collection performance,

improved RAM footprint and response to system-memory pressure, improved concurrency and support for

suspending flash erases, marking of bad sectors with continued use of the remaining good sectors (enhancing

the write-life of the devices), native data compression inside the file system design, and support for hard links.

The key features of JFFS2 are:

• Targets the Flash ROM Directly

• Robustness

• Consistency across power failures

• No integrity scan (fsck) is required at boot time after normal or abnormal shutdown

• Explicit wear leveling

• Transparent compression

Although JFFS2 is a journaling file system, it may not prevent the loss of data. The file system will remain in a

consistent state across power failures and will always be mountable. However, if the board is powered down

during a write then the incomplete write will be rolled back on the next boot, but writes that have already been

completed will not be affected.

Additional information about JFFS2 is available at:

http://sources.redhat.com/jffs2/jffs2.pdf

http://developer.axis.com/software/jffs/

http://www.linux-mtd.infradead.org/