How to restore a USB drive converted to bootable

[Dave]

On Saturday 02 May 2015 17:59:02 William A. Mahaffey III wrote:
> On 05/02/15 17:30, Polytropon wrote:
> > On Sat, 02 May 2015 17:23:13 -0453, William A. Mahaffey III wrote:
> >> On 05/02/15 16:45, Polytropon wrote:
> >>> On Sat, 02 May 2015 09:20:09 -0453, William A. Mahaffey III wrote:
> >>>> On 05/02/15 09:06, Lowell Gilbert wrote:
> >>>>> "William A. Mahaffey III" <wam at hiwaay.net> writes:
> >>>>>
> >>>>>> I am about to do some OS installs (NetBSD & OpenBSD, as it happens) on
> >>>>>> boxen under construction. I would also like to use UBCD on a flash
> >>>>>> drive to memcheck those boxen prior to installation. If I prep a USB
> >>>>>> thumb drive as either a bootable UBCD drive or an over-the-WWW
> >>>>>> installer, I wipe out the drive for its original use. Is there a way
> >>>>>> to restore the drive back to its original functionality if I wanted to
> >>>>> Is "wipe the drive and reformat" what you need to hear, or do you have
> >>>>> more requirements that you haven't made clear?
> >>>>>
> >>>> Wipe & reformat, preferably from CLI under FBSD 9.3R-p13 for
> >>>> convenience, is what I'm after. Clearly creating a bootable UBCD or
> >>>> installer will wipe out whatever was
> >>>> there before, so I just want to get back to 'virgin' USB drive.
> >>> In that case, the command
> >>>
> >>> 	# dd if=/dev/zero of=/dev/da0 bs=1m count=1
> >>>
> >>> should be fine. If there is any offending GPT metadata located
> >>> at the end of the USB drive, estimate the size and also erase
> >>> the last few MBs (use skip= to do so). There is no need to
> >>> actually zero out the _whole_ drive.
> >> *Aaaaaaaaaaaaaaahhhhh*, I wasn't sure about that (zero the whole drive),
> >> thanks :-) ....
> > There are only few significant "data zones" on the USB drive.
> > The boot sector and partition table are located at the beginning,
> > and _maybe_ GPT metadata at the end. Removing both makes the
> > remaining bits and bytes practically useless (except when you
> > take it to forensics, but you don't want to recover things
> > anyway, so the result should work for you).
> >
> > However, if you want a USB drive "new" (as in "I just bought it
> > from the shop, it's fresh out of the package!"), then you have
> > to write a MSDOS (FAT) file system, install some crapware, some
> > ridiculous "drivers", and "value added" software, maybe with
> > some spying tools, malware, nagware, and non-working "encryption"
> > tools. Add several partitions and make them smaller than the
> > real size of the drive. And add a "Facebook" link. :-)
> >
> >
> >
> 
> I was thinking of dd-ing the 1st MB or 2 off into a file, then restoring 
> from that file when done, that would skip all the extra features you 
> mention ;-). Would 1 or 2 MB be enough to get all of the FS info ? I 
> wasn't aware you didn't have to zero everything out, that simplifies 
> things a fair bit ....
> 
That might be enough if you are then going to put it in a drawer, not use
it all, then restore those same few MB later.

If you are planning on installing UBCD onto it in a some form of bootable 
filesystem them I'd suggest you need to DD *at least* the size of UBCD so
you can restore any/all existing data.
You could just DD the entire pendrive and pipe it through tar/gzip if you
really want to be able to put back exactly as you found it since you don't
really know exactly where on the drive the data is.