Linux – Choice of filesystem for GNU/Linux on an SD card

filesystemslinuxsd card

I have am embedded ARM-based system running on an SD card. It's currently Debian GNU/Linux using ext3 as filesystem. As I'm about to reinstall the system, I started wondering about changing to a more flash-friendly filesystem. I've heard about JFFS2, YAFFS2 and LogFS, and they all seem suited to the job. Which one would you recommend? Also, I've heard there have been a lot of ext4 improvements to better suit SSD disks; am I to interpret that as running ext4 should be just fine? What do I need to think especially about in that case?

I guess the usage of the system is important. But for the sake of generality, imagine it'll do standard desktop stuff (even though it is infact a small ARM-based system).

Thanks for any replies.

Edit: Wikipedia tells me (in a "citation needed" statement) that Removable flash memory cards and USB flash drives have built-in controllers to perform wear leveling and error correction so use of a specific flash file system does not add any benefit. Thus, I'm leaning towards sticking with an ext filesystem.

Best Answer

Excellent article about flash filesystems.

Important question when talking about flash filesystems is following: What is wear leveling? Wikipedia article. Basically, on flash disks you can write limited number of times until block goes bad. After that, filesystem (if there is no built-in wear leveling management on hardware, as in case of SSDs there usually is) must mark that block as invalid, and avoid using it anymore.

Typical filesystems (for example ReiserFS, NTFS, ext3 and so on) are designed for hard disks, that do not have such limitations.

JFFS2

Includes compression and elegant wear leveling protection.

YAFFS2

  • Single thing that makes the difference: short mount times, after successful umount.
  • Implements write once property: once data is written to one block, there is no need to rewrite it. This is important, as it reduces wear.

LogFS

  • Not very mature, but already included in Linux kernel tree.
  • Supports larger filesystems than JFFS2/YAFFS2 without problems.

UBIFS

  • More mature than LogFS
  • Write caching support
  • On scalability: article. On large disks, better performance than with JFFS2

ext4

If no driver or card (for example SSD drives do have internal wear leveling, at least usually) handle wear leveling, then ext4 is not the best idea, as it is not intended for raw flash usage.

Which one is the best?

Of course, it depends on usage and support. From what I read on the Internet, I would recommend UBIFS. Good support for large filesystems, mature development phase, adequate performance and no huge downsides.