Re: RPi4 died SD card weirdness?

On Sun, 23 Aug 2026, Ramiro Aceves wrote:

> Sorry, I placed commands not in the mount directory. This is the right test:
>
> netbsd-acer# pwd
> /root
> netbsd-acer# mount /dev/dk2 disco_fat/
> netbsd-acer# cd disco_fat/
> netbsd-acer# echo "this is a nightmare" > test
> netbsd-acer# ls
> EFI                             boot.cfg                        fixup4cd.dat
> LICENCE.broadcom                bootcode.bin                    fixup_cd.dat
> RPI4_UEFI_Firmware_v1.50.zip    cmdline.txt                     netbsd.img
> RPI_EFI.fd                      cmdline.txt-bak                 overlays
> RPI_EFI.fd-bak                  config.txt                      start.elf
> Readme.md                       config.txt-bak                  start4.elf
> bcm2711-rpi-4-b.dtb             dtb                             start4cd.elf
> bcm2711-rpi-400.dtb             firmware                        start_cd.elf
> bcm2711-rpi-cm4.dtb             fixup.dat                       test
> boot                            fixup4.dat
> netbsd-acer# cat test
> this is a nightmare
> netbsd-acer# cd ..
> netbsd-acer# umount disco_fat/
> netbsd-acer# pwd
> /root
> netbsd-acer# mount /dev/dk2 disco_fat/
> netbsd-acer# cd disco_fat/
> netbsd-acer# ls
> EFI                             boot.cfg                        fixup4cd.dat
> LICENCE.broadcom                bootcode.bin                    fixup_cd.dat
> RPI4_UEFI_Firmware_v1.50.zip    cmdline.txt                     netbsd.img
> RPI_EFI.fd                      cmdline.txt-bak                 overlays
> RPI_EFI.fd-bak                  config.txt                      start.elf
> Readme.md                       config.txt-bak                  start4.elf
> bcm2711-rpi-4-b.dtb             dtb                             start4cd.elf
> bcm2711-rpi-400.dtb             firmware                        start_cd.elf
> bcm2711-rpi-cm4.dtb             fixup.dat
> boot                            fixup4.dat
> netbsd-acer# cat test
> cat: test: No such file or directory
> netbsd-acer#
>

Yes, I've heard of this exact same error of some SD devices becoming
"read-only".  Back in ~2011 or so, this was reported on xda-developers in
the ViewSonic G-Tablet forums. This tablet has with 16 GB of internal storage.
Most, I believe came with eMMC, but, a few others had an SDHC device (same
capacity). And, some SDHC ones exhibited this exact same failure mode.
Android would keep writing, and as long as all the I/O was taking place on
the FS cache, it all looked OK. But the kernel would panic when it noticed
the inconsistency between the in-cache data and the on-disk stuff.

I got in touch with Pierre Ossman (Linux SDcard drivers), and he hadn't seen
this failure either, but diagnosed it as some weird HW issue.

-RVP

PS. Try seeing if a `dd' with `oflag=direct' with a very large file (10GB)
provokes an error.