[PLUG] Weird microSD failure

[Tomas Kuchta]

I do not believe that SD cards respond to pure raw block writes from dd.
Not unless the stream looks like files.

I run into the same discovery some time ago. If I remember correctly, dd
didn't overwrite the content even with random data. It could behave
different for different firmware, but I tried a few with the same result.

Tomas

On Mar 7, 2018 9:13 AM, "wes" <plug at the-wes.com> wrote:

that's only if you want to generate a certain size. otherwise it just keeps
going until it runs out of blocks to fill.

-wes

On Tue, Mar 6, 2018 at 5:08 PM, Tim Garton <garton.tim at gmail.com> wrote:

> Don't you need a "count=#" option to dd as well? Not at a computer right
> now otherwise I'd be able to check if that's the case...
>
> On Mar 6, 2018 5:02 PM, "Richard England" <rlengland at frontier.com> wrote:
>
> > On 03/06/2018 04:20 PM, Tomas Kuchta wrote:
> >
> >> Try to delete the original files first. Then create empty file using
> >> /dev/zero and copy it to the card. I bet that it will be there on the
> card
> >> and some of your original data will disappear as result.
> >>
> >> My guess is that the card controller is deduplicating your /dev/zero
> >> blocks
> >> trying to protect the card from writes.
> >>
> >> Tomas
> >>
> >> On Mar 6, 2018 7:09 PM, "Russell Senior" <russell at personaltelco.net>
> >> wrote:
> >>
> >> On Tue, Mar 6, 2018 at 3:04 AM, Russell Senior
> >>> <russell at personaltelco.net> wrote:
> >>>
> >>>> On Tue, Mar 6, 2018 at 3:01 AM, Jim Karlock <jjkarlock at gmail.com>
> >>>> wrote:
> >>>>
> >>>>> My initial attempt to google this was unsuccessful (most people
point
> >>>>>> out the write protect tab, not my problem).
> >>>>>>
> >>>>>
> >>>>> Bad switch on the write protect tab? (The tab operates a tiny
> switch.)
> >>>>>
> >>>> Nope.
> >>>>
> >>>> I can turn the switch to lock and it mounts the device read only very
> >>>> clearly.  The behavior I observe is that it happily writes /dev/zero
> >>>> over the block device, but then when I read again, the old data is
> >>>> still present.
> >>>>
> >>> For example, if I flip the tab to write protect tab to "Lock", I get
> >>> this:
> >>>
> >>> # dd if=/dev/zero of=/dev/sdc status=progress bs=1M
> >>> dd: failed to open '/dev/sdc': Read-only file system
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> >
> > |Perhaps using dd if=/dev/urandom |of=/dev/sdc status=progress bs=1M
> > ...just a thought.
> >
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