Too many FATs on USB Drive?

Question

A while ago, I wrote an image on a USB drive using something along these lines:

dd bs=4M if=/path/to/image.iso of=/dev/sdb && sync

Something must have gone terribly wrong there because after using the drive once or twice, Ubuntu didn't automount it anymore. So, I decided to overwrite the partition table first, since the image partition table is not a standard table. So I did:

dd count=1 bs=512 if=/dev/zero of=/dev/sdb && sync

After that, Ubuntu suddenly mounted the drive again and I could actually access the image. This is funny, since I basicaly erased the partition table. So, I tried:

cfdisk /dev/sdb

However, cfdisk shouted FATAL ERROR: cannot open disk drive. So, I tried gparted and created a new partition table. Now, the drive is automounted but I was suspicious of the whole thing, so I tried fsck.msdos and this is the very unsettling message I got:

prompt@prompt:~$fsck.msdos /dev/sdb
dosfck 3.0.12, 29 Oct 2011, FAT32, LFN,
Currently, only 1 or 2 FATs are supported, not 251.

However, if I check the partition table with fdisk I get no error messages, nothing, just a clean table with one partition:

Disk /dev/sdb: 4004 MB, 4004511744 bytes
218 heads, 51 sectors/track, 703 cylinders, total 7821312 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
Disk identifier: 0x00095e47

Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048     7821311     3909632    b  W95 FAT32

So, the only option I see now is zeroing out the first sector which is how all this started in the first place. I'm going to try zeroing the complete device and report back with results. Don't hesitate to give me other suggestions though.

Answer 1

Wipe the first mibibyte

It is usually enough to wipe (overwrite with zeros) the first mibibyte to get rid of data, that can confuse the programs that use or create partition tables and file systems.

You can do that with dd similar to what you did with the first 512 bytes. But dd is risky, so I would recommend mkusb, which 'wraps a safety belt around dd'. There are also other tools, that are safer than dd, for example Disks alias gnome-disks.

Zeroing out the whole drive should work, but it is slow, and will cause unnecessary wear of the memory cells. I use it only, when the drive is getting slow (in order to make it fast again and restore the margin to 'gridlock'. See this link: Pendrive lifetime

Cloning

The cloning process is very reliable, when done correctly with dd, mkusbor some other cloning tool.

So I think that your problem depends on the partition table and/or file systems, that come from the image file (image.iso), or was caused by a bad or incomplete shutdown, that corrupted the file system.

You must not unplug the USB drive while some partition on it is still mounted. It is important to let the system flush the buffers, finish writing data from RAM to the partition's file system.

Answer 2

I fixed the same error using Kde-parted.

I got this error and neither fsck.vfat nor dosfsck fixed it

So I made a new FAT, with before unmount, marked the partition, at top, device, make new FAT, or ctrl-shift-N.

Then format made a new partition and everything worked normally again.