Amount of fragmentation on memory cards

What is file fragmentation? Is it important?

File fragmentation is a feature of data storage. A file is said to be fragmented when it is stored on the media in several non-adjacent fragments instead of being stored in one contiguous chunk. As long as everything works fine, the filesystem keeps track of where each part of every file is stored and re-assembles files from fragments as needed. On rotational hard drives, fragmentation carries a performance penalty. There is no practical difference in access speeds on SSD and other flash media, like memory cards.

As long as everything works, fragmentation is not an issue. Once something fails, fragmentation makes data recovery much more complicated, at least in some scenarios. The most common case when fragmentation matters is when files are deleted from some small media or when a small media is formatted. Small media like memory cards or USB flash drives uses the FAT filesystem, on which regular filesystem reconstruction does not work with fragmented files. Larger disks, which typically use NTFS, do not suffer a decrease in recoverability.

How many files are fragmented?

Based on multiple recoveries of memory cards, the current (March 2018) data is as follows:

  • 3% of all JPEG images are fragmented. However, it is essential to distinguish between thumbnail images, which some cameras store as separate files, and high-resolution image files. The breakdown is as follows:
    • 1% of thumbnails (less than 2 MP) are fragmented
    • 5% of high-resolution images (2 MP and higher) are fragmented
  • 79% of video files are fragmented. There is a significant difference between memory cards coming from cameras, phones, and dashcam video recorders, with dashcam recorders producing close to 100% fragmentation. However, none of the real-life samples I have seen had less than 50% of its video files fragmented.

What can be done about that?

If you need recovery, my Klennet Carver will recover much of the typical fragmented video and pictures for you. The download is here. There are non-trivial system requirements, but all in all, it mostly works.

Prevention-wise,

  • Keep backups.
  • There is nothing special you need to do on a regular hard drive.
  • On a memory card used in a handheld photo camera, you can format the card every time after copying all files from it and ensuring the files are copied correctly and backed up. This will keep fragmentation at bay to some extent.
  • On a memory card used in a dash camera, there is nothing practical you can do.

Created Wednesday, March 7, 2018