[scns]

IIRC there is a reserved area in the beginning of th SD cards flash which is used for internal housekeeping. When this area is overwritten/formatted the card is bricked. [add] The size depends on the size of the card. I think it is around 32KB on cards with a capacity under 2GB.

[vbezhenar]

I do some development with dev boards and firmware stuff and regularly dd images onto SD-card without any skips or something like that. I never bricked any card.

[zinekeller]

You're right but it doesn't matter here as it is fully hidden. Unless you have an SD card with a buggy firmware or access to manufacturer-specific tool, it is not accessible even when you "deep" format it.

[jeroenhd]

The reserved areas are managed by the ARM cores running inside the SD cards. Your host machine doesn't see them.

In some SD cards you can use proprietary magical commands to communicate with the firmware and update it or ask it to mess with the hidden sections for you, but those options aren't exposed to any disk copy tool I know of.

[worthless-trash]

I'm dubious about this claim, I have completely destroyed the partition table and mkfs on the raw device...

[yrro]

Unless that was an mtd device then you weren't really writing to the raw device

[worthless-trash]

It did show up as sda.. can mtd devices show up as MTD, i thought it had to use some "MTD" app to transfer files to it.

[wtallis]

You might be thinking of MTP, used by eg. phones that don't present a block device over USB so that they can internally use a filesystem not supported by Windows; MTP is a higher-level interface more akin to a network file system protocol.

mtd is a Linux driver subsystem for accessing raw NAND or NOR flash devices that don't have an SSD's Flash Translation Layer (FTL) in front of them to provide features like wear leveling. It's most commonly encountered in embedded systems.

[worthless-trash]

You are correct, I was thinking of MTP.

Thank you for the education.

[yrro]

As I understand it there is a controller on your device that emulates a disk drive. The controller is accessing the raw device on your behalf and _should_ not be overwriting any sensitive/forbidden areas of the flash that might brick the device.