EHD>disk utility>erase 7 pass>quit on pass 4>what happens? i quit it on pass 4 (pass 3 complete), disk is being returned to store so i must wipe off the contents. is a DOE security erase level 3 is sufficient? quitting on pass 4 means pass 3 is still in tact? DU doesn't restate original data? i would do a pass 7 but i think it would take 7 or more days.
thank you for any input!
The erase is still "intact" and whether or not it's sufficient depends on your corporate procedures, I suppose. Three passes is considered DOE-compliant (Department of Energy); seven passes would be DOD-compliant (Department of Defense). You're probably fine to return the system.
Just in case you're curious, modern systems delete files by simply marking the clusters (locations on the disk) as being unused, but the data is still there. That's how some of those data recovery programs can work - assuming the operating system hasn't placed new data into those locations, the original data is still there and the links to its pieces just need to be restored. It's worth noting that this is
not the case for SSDs; older SSDs may have worked similarly, but because an SSD takes longer to overwrite something that already has data than it does to write to an unused space, modern SSDs actually purge the data when it is deleted. (This is what the TRIM command is all about.)
A secure erase actually rewrites the entire disk with random data (or with all 0's or 1's). That it needs to cover the entire disk is why it takes so long to perform. It makes it essentially impossible to recover any of the original data. The theory behind why one would need to do this multiple times is because traditional hard drives store data magnetically, and one could possibly analyze the drive's magnetic fields at each sector and determine what its previous state was. It's thought that performing multiple passes could possibly thwart such forensic analysis.
There is some pushback against the idea that multiple passes need to be performed on modern hard drives in order to securely wipe them. Disk storage densities have increased quite a bit since the theories about needing to do multiple passes were made, and it's thought that doing the magnetic field analysis would be prohibitively expensive, if not impossible.
