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From: David Empson on 26 Jul 2010 17:30
Nick Naym <nicknaym@_remove_this_gmail.com.invalid> wrote:

> In article 1jm9n8z.1qq7yjj1kqt3e4N%dempson(a)actrix.gen.nz, David Empson at
> dempson(a)actrix.gen.nz wrote on 7/26/10 10:27 AM:
>
> > Nick Naym <nicknaym@_remove_this_gmail.com.invalid> wrote:
> >
> >> I can "zero out" the _drive_ two ways: via DU's Erase tab, or via DU's
> >> Partition tab; and I can "zero out" the _volume_ one way: via DU's Erase
> >> tab.
> >>
> >> I don't know which of these 3 ways is preferred because I don't know what
> >> the differences are.
> >
> > Quite simple:
> >
> > If you use "zero out data", then Erase Drive or Partition Drive will
> > overwrite everything that was previously on the drive. Every sector of
> > the drive is overwritten with zeros.
>
> I see.
>
>
>
> > In comparison, Erase Volume will only overwrite the content area of one
> > partition on the drive.
>
>
> I've only ever had a single partition on that drive.
>
>
>
> > The partition map, other partitions, and any
> > sectors outside of partitions such as free space are NOT overwritten, so
> > there is a possibility they might contain residual data.
> >
>
> "Residual data?" Since I've never had more than one partition, what kind of
> data outside of that partition might there be?

Probably nothing.

If you ever changed the partition map scheme (between GUID Partition
Table, Apple Partition Map and Master Boot Record), then the precise
position and size of the partition on the drive will change, because the
partition map sizes are different, and some schemes have extra reserved
areas outside the partition.

There is theoretical possiblity that there could be some residual data
off either end of the partition if you changed the partition map scheme
and didn't choose to zero data that time, and haven't done an Erase
Drive or Partition Drive with zero data since then.

The data which might "leak" is most likely to be directory information,
since with HFS+ the directory is located at the start of the volume,
with a backup copy at the end of the volume.


If your intention is to erase everything on the drive, you should use
Erase with the drive selected. It will only take a very small amount of
additional time (over erasing just the volume), and ensures every sector
on the drive has been overwritten.

> > As far as Erase and Partition of the Drive are concerned:
> >
> > "Erase" of the drive is identical to using the Partition tab, selecting
> > a volume scheme of "1 partition", and NOT clicking the Options button
> > (i.e. keep the same partition map scheme).
> >
> > The Partition tab gives you more options, particularly setting up
> > multiple partitions, changing the size of the partitions, and changing
> > the partition map scheme.
> >
> > Using the Partition tab with "Current" selected as the Volume Scheme is
> > a more complex beast. Under Leopard and later, this can be used to
> > adjust existing partitions. Partitions can be added and deleted without
> > affecting the content of other partitions, and some resizing of
> > partitions is possible.


--
David Empson
dempson(a)actrix.gen.nz
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