Flash file-systems

• 'Standard' file systems are meant to work on block devices
• Specific file systems have been developed to deal flash constraints
• These file systems are relying on the MTD layer to access flash chips
• There are several legacy flash filesystems which might be useful for specific usage: JFFS2, YAFFS2.
• Nowadays, UBI/UBIFS is the de facto standard for medium to large capacity NANDs (above 128MB)

Legacy flash filesystems: JFFS2

• Supports on the fly compression
• Wear leveling, power failure resistant
• Available in the official Linux kernel
• Boot time depends on the filesystem size: doesn't scale well for large partitions.
• http://www.linux-mtd.infradead.org/doc/jffs2.html

Legacy flash filesystems: YAFFS2

• Mainly supports NAND flash
• No compression
• Wear leveling, power failure resistant
• Fast boot time
• Not part of the official Linux kernel: code only available separately (Dual GPL / Proprietary license for non Linux operating systems)
• http://www.yaffs.net/

UBI/UBIFS

• Aimed at replacing JFFS2 by addressing its limitations
• Design choices:
  • Split the wear leveling and filesystem layers
  • Add some flexibility
  • Focus on scalability, performance and reliability
• Drawback: introduces noticeable space overhead, especially when used on small devices or partitions.