[gblargg]

I'd at least just read all the used blocks on the drive. partclone is the most efficient that comes to mind, because it just copies used sectors. Just redirect to /dev/null.

    partclone.filesystem --source /dev/sdx --clone --output /dev/null

[justinclift]

If you just need to read all of the sectors, then couldn't you just dd or cat the source drive instead?