I love --data-preview in modern GNU ddrescue.
Anxiety-reducing after checking many, many times and different ways that I had the drives the right way around to see that it is indeed copying data, and not zeroes.
(The kernel had, in fact, swapped the device names after a "you fool, you tried to suspend under Linux"-induced reboot.)
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(All I need now is a --dry-run. I guess you could first-pass for a bit with an output of /dev/null...)
