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I recall once having an SD card with a mysterious file in the root folder with system and hidden attributes on it. I decided to delete the file and some time la

by billpg 2y ago

I recall once having an SD card with a mysterious file in the root folder with system and hidden attributes on it. I decided to delete the file and some time later (months), the card suddenly stopped working. It maybe stopped working once the OS decided the bytes were available for use (which it would only have done without the file marking that space as unavailable) and overwrote that section. I suspect defragmenting or otherwise moving the file about for whatever reason would have had the same effect.

karamanolev 2y ago
Wouldn't a regular filesystem format of the card have the same effect - wipe the file? Wouldn't such SD cards be fatally flawed for most applications? My camera, drone, etc. all format the cards.
- billpg 2y ago
  I vaguely recall thinking the file was just some sort of serial number or stock tracking metadata when I deleted it. It might have instead failed for quite mundane reasons such as low quality manufacture. I don't know. Exposing the firmware in this fashion would be a bad idea for all of these reasons. It is a good thing that SD card manufacturers don't do this any more, if they ever did.
  - vardump 2y ago
    Firmware definitely would not be on the filesystem layer or even accessible on the block device.
    - 01HNNWZ0MV43FF 2y ago
      You'd think yeah
      - tiberious726 2y ago
        It isn't. Before a chip has firmware loaded, it can't decode filesystems.
        15155 2y ago
        Even after a chip has firmware loaded, which controller can make logical sense of a filesystem?
        goodburb 2y ago
        According to SDXC specs, the controller looks for exFAT markers to relocate the table and bitmap to smaller AU units. exfatprogs can pack bitmap with table for SDHC and lower: https://manpages.debian.org/experimental/exfatprogs/mkfs.exfat.8.en.html https://manpages.debian.org/experimental/exfatprogs/mkfs.exf...
        samatman 2y ago
        That doesn't at all mean that the firmware can't be exposed through the filesystem. Is that a bad idea? Almost certainly. Is it possible? Absolutely yes.

by billpg 2y ago

karamanolev 2y ago

Wouldn't a regular filesystem format of the card have the same effect - wipe the file? Wouldn't such SD cards be fatally flawed for most applications? My camera, drone, etc. all format the cards.

billpg 2y ago
I vaguely recall thinking the file was just some sort of serial number or stock tracking metadata when I deleted it. It might have instead failed for quite mundane reasons such as low quality manufacture. I don't know. Exposing the firmware in this fashion would be a bad idea for all of these reasons. It is a good thing that SD card manufacturers don't do this any more, if they ever did.
- vardump 2y ago
  Firmware definitely would not be on the filesystem layer or even accessible on the block device.
  - 01HNNWZ0MV43FF 2y ago
    You'd think yeah
    - tiberious726 2y ago
      It isn't. Before a chip has firmware loaded, it can't decode filesystems.
      - 15155 2y ago
        Even after a chip has firmware loaded, which controller can make logical sense of a filesystem?
        goodburb 2y ago
        According to SDXC specs, the controller looks for exFAT markers to relocate the table and bitmap to smaller AU units. exfatprogs can pack bitmap with table for SDHC and lower: https://manpages.debian.org/experimental/exfatprogs/mkfs.exfat.8.en.html https://manpages.debian.org/experimental/exfatprogs/mkfs.exf...
      - samatman 2y ago
        That doesn't at all mean that the firmware can't be exposed through the filesystem. Is that a bad idea? Almost certainly. Is it possible? Absolutely yes.