Copying USB stick fails with device errors

[Alex]

Hi,

>> I believe the problem is that the filesystem starts at block 4 and not
>> at the beginning, so mount can't figure out how to mount it.
>
> Use an offset, e.g.
>
> # mount -o loop,offset=4 ....

Thanks, I should have thought of that. Alas, it didn't work.

# mount -o loop,offset=4 -t vfat myusb_sdb.dd /media/desktop/
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

I took the dd image I created, and dumped it directly to another USB
stick, then inserted it, and fedora automatically detected and mounted
it, just as the original.

So it's something I'm doing wrong with the mount. Does anyone have any
ideas what might be wrong with my mount command?

# dd if=/dev/sdb of=myusb_sdb.dd
dd: reading `/dev/sdb': Input/output error
5242864+0 records in
5242864+0 records out
2684346368 bytes (2.7 GB) copied, 182.722 s, 14.7 MB/s

# fdisk -l /dev/sdb

Disk /dev/sdb: 3870 MB, 3870335488 bytes
45 heads, 4 sectors/track, 41995 cylinders, total 7559249 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: 0x261e6d11

  Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           4     5242859     2621428    b  W95 FAT32

# file myusb_sdb.dd
myusb_sdb.dd: x86 boot sector; partition 1: ID=0xb, active, starthead
1, startsector 4, 5242856 sectors, code offset 0x31

Running fdisk on myusb_sdb.dd returns the same as the original device:

# fdisk -l myusb_sdb.dd

Disk myusb_sdb.dd: 2684 MB, 2684346368 bytes
45 heads, 4 sectors/track, 29127 cylinders, total 5242864 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: 0x261e6d11

       Device Boot      Start         End      Blocks   Id  System
myusb_sdb.dd1   *           4     5242859     2621428    b  W95 FAT32

Thanks for any ideas,
Alex