I counter-speculate that this is a failure mode of flash storage: the controller onboard the storage device is able to accept writes into its cache, but fails to flush the cache to the actual storage media.
-wes On Sun, May 10, 2026 at 6:09 AM Tomas Kuchta <[email protected]> wrote: > I have experienced this before and not really understood it, due to the > lack of patience and finding a workaround. > > My workaround was to use the Raspberry Pi imager writing what I needed to > the SD card. I believe, if my memory serves me well, that Balena Etcher was > also successful at writing to these SD cards. Both imagers run on Linux. > > From that - I guess that you can repartition the SD then write normal data > from /dev/zero to the partitions. > > My wild guess was that the SD card firmware will block if trying to write > outside the partitions boundaries. Perhaps to protect itself from being > owerwritten. That is my speculation though. > > -T > > On Sat, May 9, 2026, 23:47 Russell Senior <[email protected]> > wrote: > > > On Sat, May 9, 2026 at 3:56 PM Ted Mittelstaedt <[email protected]> > > wrote: > > > > > > Have you tried a different card reader in a different computer? > > > > I think I literally said that in the second paragraph, but yes. On > > plugging via a USB dongle, dmesg says it is writable: > > > > [Sat May 9 20:06:58 2026] usb 3-2: new high-speed USB device number > > 18 using xhci_hcd > > [Sat May 9 20:06:58 2026] usb 3-2: New USB device found, > > idVendor=05e3, idProduct=0751, bcdDevice=14.04 > > [Sat May 9 20:06:58 2026] usb 3-2: New USB device strings: Mfr=3, > > Product=4, SerialNumber=0 > > [Sat May 9 20:06:58 2026] usb 3-2: Product: USB Storage > > [Sat May 9 20:06:58 2026] usb 3-2: Manufacturer: USB Storage > > [Sat May 9 20:06:58 2026] usb-storage 3-2:1.0: USB Mass Storage device > > detected > > [Sat May 9 20:06:58 2026] scsi host0: usb-storage 3-2:1.0 > > [Sat May 9 20:06:59 2026] scsi 0:0:0:0: Direct-Access Generic > > STORAGE DEVICE 1404 PQ: 0 ANSI: 6 > > [Sat May 9 20:06:59 2026] sd 0:0:0:0: Attached scsi generic sg0 type 0 > > [Sat May 9 20:06:59 2026] sd 0:0:0:0: [sda] 31116288 512-byte logical > > blocks: (15.9 GB/14.8 GiB) > > [Sat May 9 20:06:59 2026] sd 0:0:0:0: [sda] Write Protect is off > > [Sat May 9 20:06:59 2026] sd 0:0:0:0: [sda] Mode Sense: 21 00 00 00 > > [Sat May 9 20:06:59 2026] sd 0:0:0:0: [sda] Write cache: disabled, > > read cache: enabled, doesn't support DPO or FUA > > [Sat May 9 20:06:59 2026] sda: sda1 > > [Sat May 9 20:06:59 2026] sd 0:0:0:0: [sda] Attached SCSI removable disk > > [Sat May 9 20:07:00 2026] EXT4-fs (sda1): recovery complete > > [Sat May 9 20:07:00 2026] EXT4-fs (sda1): mounted filesystem > > 40af6f66-8d84-45b4-b056-9a2ee4c5a7b5 r/w with ordered data mode. Quota > > mode: none. > > > > umount /dev/sda1 > > > > [Sat May 9 20:08:02 2026] EXT4-fs (sda1): unmounting filesystem > > 40af6f66-8d84-45b4-b056-9a2ee4c5a7b5. > > > > # time dd if=/dev/urandom of=/dev/sda bs=128k status=progress oflag=sync > > 15921446912 bytes (16 GB, 15 GiB) copied, 863 s, 18.4 MB/s > > dd: error writing '/dev/sda': No space left on device > > 121549+0 records in > > 121548+0 records out > > 15931539456 bytes (16 GB, 15 GiB) copied, 863.936 s, 18.4 MB/s > > > > real 14m23.938s > > user 0m0.749s > > sys 2m5.471s > > > > [Sat May 9 20:23:31 2026] sda: sda1 > > > > like, why is there still a partition? > > > > # time dd if=/dev/zero of=/dev/sda bs=128k status=progress oflag=sync > > 15915155456 bytes (16 GB, 15 GiB) copied, 751 s, 21.2 MB/s > > dd: error writing '/dev/sda': No space left on device > > 121549+0 records in > > 121548+0 records out > > 15931539456 bytes (16 GB, 15 GiB) copied, 752.161 s, 21.2 MB/s > > > > real 12m32.163s > > user 0m0.634s > > sys 0m19.809s > > > > [Sat May 9 20:36:49 2026] sda: sda1 > > > > Unplug and replug, dmesg says: > > > > [Sat May 9 20:39:21 2026] usb 3-2: USB disconnect, device number 18 > > [Sat May 9 20:39:25 2026] usb 3-2: new high-speed USB device number > > 19 using xhci_hcd > > [Sat May 9 20:39:25 2026] usb 3-2: New USB device found, > > idVendor=05e3, idProduct=0751, bcdDevice=14.04 > > [Sat May 9 20:39:25 2026] usb 3-2: New USB device strings: Mfr=3, > > Product=4, SerialNumber=0 > > [Sat May 9 20:39:25 2026] usb 3-2: Product: USB Storage > > [Sat May 9 20:39:25 2026] usb 3-2: Manufacturer: USB Storage > > [Sat May 9 20:39:25 2026] usb-storage 3-2:1.0: USB Mass Storage device > > detected > > [Sat May 9 20:39:25 2026] scsi host0: usb-storage 3-2:1.0 > > [Sat May 9 20:39:26 2026] scsi 0:0:0:0: Direct-Access Generic > > STORAGE DEVICE 1404 PQ: 0 ANSI: 6 > > [Sat May 9 20:39:26 2026] sd 0:0:0:0: Attached scsi generic sg0 type 0 > > [Sat May 9 20:39:27 2026] sd 0:0:0:0: [sda] 31116288 512-byte logical > > blocks: (15.9 GB/14.8 GiB) > > [Sat May 9 20:39:27 2026] sd 0:0:0:0: [sda] Write Protect is off > > [Sat May 9 20:39:27 2026] sd 0:0:0:0: [sda] Mode Sense: 21 00 00 00 > > [Sat May 9 20:39:27 2026] sd 0:0:0:0: [sda] Write cache: disabled, > > read cache: enabled, doesn't support DPO or FUA > > [Sat May 9 20:39:27 2026] sda: sda1 > > [Sat May 9 20:39:27 2026] sd 0:0:0:0: [sda] Attached SCSI removable disk > > [Sat May 9 20:39:27 2026] EXT4-fs (sda1): recovery complete > > [Sat May 9 20:39:27 2026] EXT4-fs (sda1): mounted filesystem > > 40af6f66-8d84-45b4-b056-9a2ee4c5a7b5 r/w with ordered data mode. Quota > > mode: none. > > > > wtf? > > > > Same thing seems to be happening on another micro SD card on an mmcblk > > interface on a different computer. > > > > > > Sent: Saturday, May 9, 2026 2:15 PM > > > To: Portland Linux/Unix Group <[email protected]> > > > Subject: [PLUG] writing to micro SD card and not writing to micro SD > > cards AT THE SAME TIME??? > > > > > > I was trying to reformat some microSD cards last night. They are > > apparently writable, mount rw. I umount them, use (CAREFULLY) dd to write > > /dev/zero or /dev/urandom on to them and dd seems to happily do it. I can > > even hexdump back out the zeros or whatever back out, for a short time. > But > > moments later, all the original content is still there. > > > > > > I have tried multiple computers, two different microSD cards, multiple > > distribution versions, interface adapters, including your usual USB > > adapters and mmcblk adapters, same result. It isn't a write protect slide > > switch, because there aren't any in some of those adapters and anyway, in > > the case where there was one, it was in the correct position. > > > > > > Anyone know what's going on? > > > > > > -- > > > Russell Senior > > > [email protected] > > > > > >
