A presentation on file systems for mobile phones.

1. File Systems for Mobile Phones or
Handheld Devices
By
Ram Kumar K R
Ganesh Arkalgud

2. Introduction
• Flash Storage
• Linux Flash File Systems
• Flash Transition Layer

3. Linux Flash File Systems
• JFFS – Journaling Flash File System
• JFFS2 – Journaling Flash File System 2
• YAFFS – Yet Another Flash File System
• UBIFS – Unsorted Block Image File System
• F2FS – Flash Friendly File System

4. TrueFFS
• Patented flash management software
• By M – Systems
• Software layer between OS’ File System and
Hardware.
• Provides block device functionality and flash
media management

5. TrueFFS Structure

6. JFFS2
• Log-structured open-source file system
• NAND and OneNANDTM Flash memory devices
• Developed and maintained within the
Memory Technology Device (MTD) layer
• Garbage collection
• Wear leveling
• Power loss recovery

7. JFFS 2 Structure

8. YAFFS
• Yet Another Flash File System
• NAND model – chunks and blocks
• Linux, RTOS and devices with no OS
• YAFFS1
• YAFFS2

10. YAFFS Directory Structure

11. • Tree of objects of type
YAFFS_OBJECT_TYPE_DIRECTORY.
• not stored in NAND but are instead created on
mounting
• lost+found
• Unlinked and deleted

12. UBIFS
• For Raw – Flash Systems
• Fix JFFS 2 Issues such as
• Faster mount
• Fast opening of big files
• Faster write speed
• Maps Physical Erase Blocks(PEB) to Logical Erase
Blocks(LEB)
• Disadvantages
• Scales Linearly
• Reads all block headers during initialization
• Time for initialization increases with flash size

15. Flash Transition Layer
• Makes flash appear as a disk drive for OS
• Enables mounting FAT, ext and other file
systems on to a flash drive.

17. F2FS
• Assumes presence of Flash Transition Layer
• Log – structured design
• On disk layout - Block (4K in size) Segment
(2MB in size) Section (consecutive segments)
Zone (set of sections) Area (multiple sections)
Volume (six areas)

19. Test Results of F2FS

20. iOS File System
• Each app is an island
• Public system interfaces

22. A Distributed File System for Mobile
Computing
• Efficient variable consistency replication
• Intelligent file prefetching
• Trade off between availability and consistency

23. References
• www.yaffs.net
• Software Profile: Journaling Flash File System, Version 2 (JFFS2) By
Luca Boschetti,Micron Software Engineer
• TrueFFS® 6.x Software Development Kit (SDK) Quick Reference
Guide
• iOS File System Programming Guide by Apple Inc.
• UBIFS file system by Adrian Hunter and Artem Bityutskiy, Nokia
Corporation
• Understanding the Flash Translation Layer (FTL) Specification by
intel corporation.
• Flash Friendly File System overview by Leon Romanovsky
• A Ph.D thesis on File System for Mobile computing, by Dr. Carl
Downing Tait