> I'm assuming the reason this works is because the underlying block that gets written isn't the same one that has the old data and thus the probability of overwriting with the same data is low because the encryption key for a given write is somehow derived from block offset
No, this has nothing to do with writing the same data to the same blocks, but rather how you handle a continuous stream of data being written (and eventually overwriting older data) to the drive over very long periods of time. You should assume that physical location of your data bears zero correlation to the address to write it to. The SSD controller will always redirect it to least worn available block.
In SSD it’s reasonable to assume that the flash memory can be erased and written at a more granular level than you would want to track for wear levelling purposes (because extra granularity cost more money). So writing repeated patterns of data to a disk that align with the wear levelling block size will result in some parts of your flash memory being written and erased more often. But this unevenness is too granular for the wear levelling algorithm to track and compensate for. Encryption removes the need to track more granular wear patterns because it ensures that every single bit of your flash memory is going to see very similar write patterns.
Additionally there’s an entirely separate aspect, which is that NAND flash is a physical storage medium, and economics mean manufacturers want to squeeze every last ounce of storage out of their silicon. This means pack flash cells physically close to each other, and storing multiple values in each cell. The consequence is that activity in one cell can cause changes in adjacent cells, if those changes are large enough value of a cell will change corrupting the stored data.
By encrypting the data you can eliminate the possibility of extreme edge cases occurring which have a high risk of data corruption. At better place to observe these types of issues is to look at RAM, and Row Hammer attacks. The basic principles are the same, even if the precise physical interactions are a little different.
I'm assuming the reason this works is because the underlying block that gets written isn't the same one that has the old data and thus the probability of overwriting with the same data is low because the encryption key for a given write is somehow derived from block offset + length to make sure that a duplicate pattern for a given block will still encrypt differently?
If I understood that properly, this feels like a lot of complexity for unclear gain (not seeing how it improves write leveling vs at best downgrading the best case / average case to the worst case) and I haven't found any papers online. Is this mechanism something you actually first hand building or something you remember reading from some tech newspaper? Would love a primary source here.