I'm seeing about 15% slower raw speed than the bare drive, dd if=/dev/zero of=tmp bs=1M count=512 is giving me between 68 and 250 mb/sec on a 2013 MBA with a ne

I'm seeing about 15% slower raw speed than the bare drive, dd if=/dev/zero of=tmp bs=1M count=512 is giving me between 68 and 250 mb/sec on a 2013 MBA with a nearly full disk, where in the terminal I'm getting between 78mb/s and 290mb/s. ymmv, of course.