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 > _______________________________________________ > PLUG mailing list > PLUG@pdxlinux.org > http://lists.pdxlinux.org/mailman/listinfo/plug > _______________________________________________ PLUG mailing list PLUG@pdxlinux.org http://lists.pdxlinux.org/mailman/listinfo/plug