Worthy theories.

I tried deleting the files in the second partition (rootfs), the OS
said they were gone.  When I umounted, unplugged, replugged, they were
all there again.

I tried writing over the first 1.5GB of blocks (I got impatient and
control-C'd it after about 5 minutes) with /dev/urandom, sync'd,
unplugged, replugged, my partition table was intact, and my files in
rootfs were intact.

I think it is likely that the card controller is dysfunctional, but
why or how is a good question.

On Tue, Mar 6, 2018 at 5:12 PM, wes <p...@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....@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" <rlengl...@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" <russ...@personaltelco.net>
>> >> wrote:
>> >>
>> >> On Tue, Mar 6, 2018 at 3:04 AM, Russell Senior
>> >>> <russ...@personaltelco.net> wrote:
>> >>>
>> >>>> On Tue, Mar 6, 2018 at 3:01 AM, Jim Karlock <jjkarl...@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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