Thank you for clarification. I was about to bet on "read fail repeat skip" cycle for dd's behaviour but, looking into coreutil's source code at https://github.

Thank you for clarification. I was about to bet on "read fail repeat skip" cycle for dd's behaviour but, looking into coreutil's source code at https://github.com/goj/coreutils/blob/master/src/dd.c https://github.com/goj/coreutils/blob/master/src/dd.c , if I'm not mistaken , dd does not try to be intelligent and just uses a zeroed out buffer so It would return 0's for unreadable blocks.