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.
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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