Date: Tue, 4 Aug 2015 01:41:59 +0200 From: Polytropon <freebsd@edvax.de> To: jd1008 <jd1008@gmail.com> Cc: freebsd-questions@freebsd.org Subject: Re: USB stick and some help with it. Message-ID: <20150804014159.33ed75f0.freebsd@edvax.de> In-Reply-To: <55BFF992.6010309@gmail.com> References: <55BF6AA0.2030802@bananmonarki.se> <20150804003056.094ffc57.freebsd@edvax.de> <55BFF992.6010309@gmail.com>
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On Mon, 03 Aug 2015 17:30:26 -0600, jd1008 wrote:
> Since a CD or DVD iso was dd'ed to this stick,
> OS thinks it IS an optical ROM device - and thus
> not writable.
Nah... that sounds stupid... :-)
To the OS, the USB stick is represented as a direct access
("da") media without "implicit" write protection. That's why
it should be possible to write to the _device_ - keep in
mind the device is agnostic of the file system (which is
something happening at a "higher level").
Optical devices are usually controlled by the "cd" driver
which also doesn't have an "implicit" understanding of
write protection. The fact that a media cannot be written
to can originate from (basically) two reasons:
a) The media (CD, DVD) cannot be written to, because
it physically does not allow it.
b) The drive cannot write, because it doesn't have that
capability.
The same applies to "da" type media, but is much less
common due to the nature of the _actual_ media in use
in such devices.
However, in today's USB sticks, there's much more "firmware
magic" than in a CD/DVD writer. In fact, there's a whole
computer inside, and it _might_ be possible that the
controller is somehow "clever" and refuses writing as
it has "learned" that it holds a CD image. Additionally,
the firmware can be programmed, and it can be programmed
to represent to the system not as a "da" device as you
would assume, but as a "cd" device instead. You sometimes
find this behaviour in USB sticks that need "drivers" to
operate (usually found in "Windows" land): If inserted,
it poses as a CD drive, urging you to install the drivers
that _then_ tell the PC to turn the USB stick into its
"normal" mode. There are also WLAN or UMTS dongles that
use a similar mechanism to offer its drivers "per USB CD"
to the PC, but those usually don't have the ability to
be used as a normal USB stick (for storage).
> Same issue happened to me and fixed the stick
> by using a linux pc to dd /dev/zero into the stick.
That should work - except, of course, the USB stick has
been "bricked" and cannot be written to anymore. This
may sound stupid as well, but it's possible, as explained.
--
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...
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