Data life guard diagnostics quick or full erase?

WD Software WD Software
1

QUICK ERASE writes zeros to the first and last million sectors of the drive
FULL ERASE writes zero to the entire drive

  1. when should i use quick or full erase?
  2. how does quick erase works? why would it writes zeros to the first and last million sectors of the drive? why the value isn’t thousand or hundred, but million?
2

  1. This is up to your needs. A quick erase is good-enough to reset the hard drive to a clean condition, with no file system or partition table. A full erase ensures all traces of data are gone.

  2. A typical 320GB hard drive has around 671 million 512b sectors, or 83.87 million 4K sectors. Hard drives are filled with data in layers, starting from the surface, and then deeper layers. As such, the first and last million sectors are the ones to be filled-out with data first.