Or instead of files just write to the block device with one big random file with the supposed byte-accurate size of the device, then read it back and compare. S

Or instead of files just write to the block device with one big random file with the supposed byte-accurate size of the device, then read it back and compare. Something like: dd bs="$(blockdev --getsize64 "$device")" count=1 if=/dev/urandom of=random-file dd if=random-file of="$device" cmp random-file "$device" Using cmp instead of something like md5sum is better since it would stop on the first differing byte, instead of reading the whole thing for both. EDIT: I'm not sure if my use of dd's bs and count is a good idea, though. It might be better to do: head -c "$(blockdev --getsize64 "$device")" /dev/urandom > random-file to get more reasonable buffer sizes. Documentation on head says -c works on bytes, not characters, so that's good. For that second line, I often prefer to do: pv random-file > "$device" to get a neat progress bar. EDIT 2: As discussed in other threads, one should make sure to invalidate the kernel's cache of the device between steps 2 and 3. My safest bet on how to do that is to reboot the computer.