This information is stored in a reserved space, on the same chips as your data. There are also other bits that can go wrong (becoming unchangeable, unsettable, or unclearable), these parts must be marked faulty as well during the lifetime. Typically a part of flash storage is faulty, and is marked so during manufacturing. However, due to how the internals of a flash drive are built, if you use a single overwrite pass, there may be several layers of data hidden behind the actual blocks that are still storing leftover information.

In theory, overwriting with zero with dd is just fine. Shred: /dev/sdXX: pass 9/9 (000000).3.8GiB/3.8GiB 100%īlkdiscard: /dev/sdXX: BLKSECDISCARD ioctl failed: Operation not supportedīlkdiscard: /dev/sdXX: BLKDISCARD ioctl failed: Operation not supported In these checks, always use the drive (like /dev/sd h) and not the partition name (which would be /dev/sd h1) # dmesg|grep sdXX You can follow it by an erase command designed for flash hardware, if you are on a recent enough distribution. TL/DR: Make sure you get the right device name, ensure it's not mounted, and do as many random overwrites as you can afford.

How to erase a flash drive memory