shred doesn’t even necessarily work at the OS level. If you use something like ext3 and I assume ext4, normally when you overwrite data in a file, you’re not overwriting data even at the logical level in the block device. Journalling entails that you commit data to somewhere else on the disk, then update the metadata atomically to reference the new data.
the shred command in Linux tries to do this, but it may not work if the hardware moves rewritten data blocks around to mitigate wear.
shreddoesn’t even necessarily work at the OS level. If you use something likeext3and I assumeext4, normally when you overwrite data in a file, you’re not overwriting data even at the logical level in the block device. Journalling entails that you commit data to somewhere else on the disk, then update the metadata atomically to reference the new data.