[SOLVED] can SD card fail this way?

lvm_ · 02-21-2021, 01:24 PM

Bona fide "32G" SD card which did successfully hold 29G of data suddenly started accepting no more than 4G. It happened when I tried to write partition image to it:

Code:

# dd if=car.sd.sandisk.dd of=/dev/sdj1 bs=16384
dd: error writing '/dev/sdj1': No space left on device
248773+0 records in
248772+0 records out
4075892736 bytes (4.1 GB, 3.8 GiB) copied, 20.7289 s, 197 MB/s

Always fails at exactly the same place after 4075892736 bytes. When I tried to re-create filesystem it created a 4G one

Code:

# /sbin/mkfs.vfat -v /dev/sdj1
mkfs.fat 4.1 (2017-01-24)
Auto-selecting FAT32 for large filesystem
/dev/sdj1 has 255 heads and 63 sectors per track,
hidden sectors 0x0000;
logical sector size is 512,
using 0xf8 media descriptor, with 7960728 sectors;
drive number 0x80;
filesystem has 2 32-bit FATs and 8 sectors per cluster.
FAT size is 7760 sectors, and provides 993147 clusters.
There are 32 reserved sectors.
Volume ID is cb2429a9, no volume label.

even though partition is a 29G one

Code:

Command (m for help): p
Disk /dev/sdj: 29 GiB, 31104958464 bytes, 60751872 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device     Boot Start      End  Sectors Size Id Type
/dev/sdj1        8192 60751871 60743680  29G  c W95 FAT32 (LBA)

Ok, flash cards do fail - nothing unusual here, but two things make me suspicious: there are no messages in syslog about bad sectors and such - no errors at all, and the writing speed of the image is way too high - it is a Class 10 card good for 10 MB/sec, not 200. I am on ubuntu 18.04, and there is some background automount trickery goes on for usb devices. So... am I missing something?

teckk · 02-21-2021, 02:03 PM

Quote:

dd if=car.sd.sandisk.dd of=/dev/sdj1 bs=16384

You wrote to a partition and not the device.

What is the output of, with the device plugged in.

Code:

fdisk -l
lsblk
parted -l

Quote:

/sbin/mkfs.vfat -v /dev/sdj1

That's a partition. How large is it? Is there free space on the device? Other partitions?

Edit:
Oh I see, didn't read good enough.

If you are sure that /dev/sdj is the usb device

Code:

dd if=/dev/zero of=/dev/sdj bs=1M count=10

Then start over. That will wipe the partition table.

Brains · 02-21-2021, 05:29 PM

If it has FAT32 file system, largest file size is 4GB. If you want to write larger files like a 16GB flash drive image perhaps, you need to use a different file system on the destination drive. Like extFAT, ext4, ntfs

Quote:

Device Boot Start End Sectors Size Id Type
/dev/sdj1 8192 60751871 60743680 29G c W95 FAT32 (LBA)

lvm_ · 02-22-2021, 03:23 AM

Here is what lsblk and parted say about it - consistent with fdisk which was in my original message.

Code:

sdj       8:144  1   29G  0 disk  
└─sdj1    8:145  1   29G  0 part  


Model: Generic Ultra HS-SD/MMC (scsi)
Disk /dev/sdj: 31.1GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start   End     Size    Type     File system  Flags
 1      4194kB  31.1GB  31.1GB  primary  fat32        lba

And zeroing and re-creating partition table have no effect at all. The thing that baffles me most is the write speed - there is no way it can write to a fairly slow SD card that fast, and AFAIK there could be no write-back caching when writing directly to a device. Or could it? - another weird thing I noticed is that for some reason df refers to this card not as /dev/sdj1 but as /dev/loop0

Code:

/dev/loop0         3972588           4    3972584   1% /media/lvm/FE30-5469

although mount sees it as /dev/sdj1 and doesn't mention /dev/loop0 at all

Code:

/dev/sdj1 on /media/lvm/FE30-5469 type vfat (rw,nosuid,nodev,relatime,uid=1000,gid=1000,fmask=0022,dmask=0022

and udisksd doesn't mention loop0 either in syslog messages

Code:

udisksd[877]: Mounted /dev/sdj1 at /media/lvm/FE30-5469 on behalf of uid 1000

When, however, I write to /dev/sdj write speed is the expected ~10 MB/sec. So what's happening here?

Quote:

Originally Posted by Brains

If it has FAT32 file system, largest file size is 4GB. If you want to write larger files like a 16GB flash drive image perhaps, you need to use a different file system on the destination drive. Like extFAT, ext4, ntfs

What filesystem limitations have to do with inability to write to a block device where it is stored? Nothing at all. I didn't even try to access the filesystem yet.

rknichols · 02-22-2021, 08:35 AM

Quote:

Originally Posted by lvm_

another weird thing I noticed is that for some reason df refers to this card not as /dev/sdj1 but as /dev/loop0

Code:

/dev/loop0         3972588           4    3972584   1% /media/lvm/FE30-5469

although mount sees it as /dev/sdj1 and doesn't mention /dev/loop0 at all

That looks like you might have accidentally created an ordinary file named "sdj1" in the /dev directory, and the 4GB size limit you are seeing is just the maximum size of the pseudo-filesystem mounted on /dev.

lvm_ · 02-22-2021, 09:08 AM

Quote:

Originally Posted by rknichols

That looks like you might have accidentally created an ordinary file named "sdj1" in the /dev directory, and the 4GB size limit you are seeing is just the maximum size of the pseudo-filesystem mounted on /dev.

Indeed I am. You are a genius, sir.