[Macpartners] Zeroing sectors of just one volume (on a partitioned drive)

[Kerem B Limon]

Quoting Timothy Boyden <trboyden at MIT.EDU>:

> Although not free, SuperScrubber from Jiiva Software 
> (http://www.jiiva.com) $29.99 claims to securely erase data from 
> internal or external hard drives and partitions.
> 
> Honestly I'm not sure how secure this approach would be given that due 
> to defragmentation data gets written all over a hard drive so even if 
> you did zero just one partition, data from that partition may still be 
> on other parts of the drive and recoverable through professional means.
> 

Um, no. Fragmantation is an issue that occurs at a higher level (filesystem)
than the logical arrangement of the disk (LBA or CHS sectors), and is in fact
filesystem-dependent because it is a result of the method used to index/store
data logically within a partition. A logical partition does indeed map to a
contiguous region (or rather, sequence) of sequential sectors and can in fact
be treated as a separate entity with clearly demarcated borders.

> A better approach would be to copy the data you want to keep to another 
> drive, zero the old drive and copy the saved data back to the old drive. 
> It's going to take awhile to zero the drive anyways so the extra step of 
> copying the good data won't mean much in the end. Also it's a safer 
> method given something could happen to the good data during the zeroing 
> process of the one partition.
> 

It is entirely possible to write code that would do what David wants, but
confine it to the data bits (not the boot sectors) of partitions. It's a really
good question and I'd be surprised if there isn't a product for it yet.

-Kerem


> Tim Boyden
> MIT Department of Facilities
> IT Group
> 
> David M Rosenberg wrote:
> 
> >With Apple's Disk Utility (version 10.4.4 in MacOS X 10.3.9), when
> >you go to erase an entire drive there is an "Options..." button that
> >has checkboxes for the following two options:
> >
> >Zero all data (writes zeros to all sectors of disk)
> >
> >8 Way Random Write Format
> >(writes random data over entire disk eight times)
> >
> >However, if I go to erase one volume on a disk drive, the "Options..."
> >button is disabled and I don't see a way of zeroing all the sectors of
> >just one volume.
> >
> >Does anyone know how to zero all the sectors of one volume without
> >effecting other volumes on the same drive with either Apple's Disk
> >Utility or some other free utility?
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> >  
> >
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Kerem B. Limon
kerem.limon at mit.edu /e-mail