Hi jggimi,
Thanks for the example. I missed the
count=n option when I read
dd(1).
It turns out that this drive
wasn't actually written correctly, in spite of the fact that it appeared OK on visual inspection.
The initial
sha256(1) checksum comparison failed. Running
cmp(1) revealed 40 errors.
I re-wrote the drive and now the checksums match.
Lesson: Appearances are deceiving. If byte-for-byte accuracy is important, run a checksum.