I am not as proficient as I am sure most of you are in the mechanics  
and science of data layout and retrieval on hard drives.

I have used Ontrack for a variety of times to retrieve data and  
assumed it was from raw scraping for data that had lost the pointers.   
When the drive had been formatted, I sometimes still had success in  
getting data off.

I one time took a training session for a SAN environment with EMC, and  
a number of DEA agents were there as well also attending the classes.   
Afterwards, we hit the pub and they told me they can retrieve data up  
to 37 layers of writes.  Now, that may not mean anything without the  
documented who/how/show-me details around here, but I can't imagine a  
DEA agent to arbitrarily lie about such details when I am beating him  
in billiards.

I asked what application he uses but he only told me it goes on  
measuring layers of degraded information left on the drive.  He  
wouldn't tell me more.

For what its worth....