[PLUG] Weird microSD failure

Russell Senior russell at personaltelco.net
Wed Mar 7 04:29:17 UTC 2018


https://www.youtube.com/watch?v=r3GDPwIuRKI

On Tue, Mar 6, 2018 at 8:22 PM, Russell Senior
<russell at personaltelco.net> wrote:
> Yeah, I understood about the on-SD controller.  There is typically
> some kind of ARM-based microcontroller that does all the block-device
> to NAND translation.  It is doing something wrong and clearly
> dysfunctional now, though.  I am sure that I did successful block
> operations on the same microSD previously.
>
> On Tue, Mar 6, 2018 at 5:31 PM, Tomas Kuchta
> <tomas.kuchta.lists at gmail.com> wrote:
>> When I said card controller, I meant the card controller on/in the actual
>> SD card. Not the piece of HW attached to your computer.
>>
>> My conclusion at the time I was trying to understand the same behavior was
>> that the in-card controller must be doing file transactions of some kind.
>> Not behaving quite like basic block device.
>>
>> I recall even trying to actively corrupt the card's content, no success.
>> Still, all worked fine when installing Linux on said cards.
>>
>> Hope it helps you avoiding wasting whole day or three on this, like I did.
>>
>> Tomas
>>
>> On Mar 7, 2018 9:23 AM, tomas.kuchta.lists at gmail.com wrote:
>>
>>> 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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