"HD 20 Test" version 1.1 has a data-destructive, low-level formatting
feature that can be used for this.
The low-level formatting feature of "HD 20 Test" version 1.1 is hidden. To
access it:
1) Launch the program.
2) When the main dialog appears, press "Command-D", and a new dialog
appears. This dialog displays what is actually happening during the
diagnostic cycle. It also provides more detailed options.
3) Click the radio button marked "Dstrct" at the lower right of the dialog
box to perform a data-destructive, low-level format on the drive (all
zeros are written to every block).
Note
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A 24-hour extended diagnostic test is also available with "HD 20 Test"
version 1.1 as a hidden feature. Press "Command-E" when the main dialog
appears to access this feature.