dd effect on cloning of iso file to usb stick

[jb]

Hi,

could you please explain what happened to the iso cloning ?

$ ls -al Downloads/
-rw-r--r--  1 jb jb 599785472 Oct  2 22:39 archlinux-2014.10.01-dual.iso

The iso size is 572M.
Verified sha1sum.

My usb stick:
$ dmesg
...
[Thu Oct  2 07:59:24 2014] usb-storage 1-1:1.0: USB Mass Storage device detected
[Thu Oct  2 07:59:24 2014] scsi4 : usb-storage 1-1:1.0
[Thu Oct  2 07:59:25 2014] scsi 4:0:0:0: Direct-Access     SanDisk  Cruzer 
         8.02 PQ: 0 ANSI: 0 CCS
[Thu Oct  2 07:59:25 2014] sd 4:0:0:0: [sdb] 7913471 512-byte logical
blocks: (4.05 GB/3.77 GiB)
[Thu Oct  2 07:59:25 2014] sd 4:0:0:0: [sdb] Write Protect is off
...

# dd if=/dev/zero of=/dev/sdb
dd: writing to ‘/dev/sdb’: No space left on device
7913472+0 records in
7913471+0 records out
4051697152 bytes (4.1 GB) copied, 1024.08 s, 4.0 MB/s

$ lsblk
...
sdb      8:16   1  3.8G  0 disk 
...
$ lsblk -f
...
sdb
...
    
# dd bs=4M if=Downloads/archlinux-2014.10.01-dual.iso of=/dev/sdb && sync
143+0 records in
143+0 records out
599785472 bytes (600 MB) copied, 157.154 s, 3.8 MB/s

$ lsblk
...
sdb      8:16   1  3.8G  0 disk 
├─sdb1   8:17   1  572M  0 part 
└─sdb2   8:18   1   31M  0 part 
...
$ lsblk -f
...
sdb    iso9660 ARCH_201410 2014-10-01-05-00-04-00               
├─sdb1 iso9660 ARCH_201410 2014-10-01-05-00-04-00               
└─sdb2 vfat    ARCHISO_EFI A05B-32C8                            
...

# fdisk -l /dev/sdb

Disk /dev/sdb: 3.8 GiB, 4051697152 bytes, 7913471 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: 0x574a1394

Device     Boot Start     End Sectors  Size Id Type
/dev/sdb1  *        0 1171455 1171456  572M  0 Empty
/dev/sdb2         252   63739   63488   31M ef EFI (FAT-12/16/32)

# mount -t auto /dev/sdb1 /mnt
mount: /dev/sdb1 is write-protected, mounting read-only
# ls -al /mnt
total 14
drwxr-xr-x  1 root root 2048 Oct  1 06:58 .
drwxr-xr-x 18 root root 4096 Sep  5 07:23 ..
drwxr-xr-x  1 root root 2048 Oct  1 06:59 arch
drwxr-xr-x  1 root root 2048 Oct  1 06:58 EFI
drwxr-xr-x  1 root root 2048 Oct  1 06:58 isolinux
drwxr-xr-x  1 root root 2048 Oct  1 06:58 loader
# ls -al /mnt/EFI/
total 1634
drwxr-xr-x 1 root root   2048 Oct  1 06:58 .
drwxr-xr-x 1 root root   2048 Oct  1 06:58 ..
drwxr-xr-x 1 root root   2048 Oct  1 06:58 archiso
drwxr-xr-x 1 root root   2048 Oct  1 06:58 boot
-rw-r--r-- 1 root root 771136 Oct  1 06:58 shellx64_v1.efi
-rw-r--r-- 1 root root 893184 Oct  1 06:58 shellx64_v2.efi

# mount -t auto /dev/sdb2 /media/
# ls -al /media/
total 24
drwxr-xr-x  4 root root 16384 Jan  1  1970 .
drwxr-xr-x 18 root root  4096 Sep  5 07:23 ..
drwxr-xr-x  4 root root  2048 Oct  1 06:58 EFI
drwxr-xr-x  3 root root  2048 Oct  1 06:58 loader
# ls -al /media/EFI/
total 1650
drwxr-xr-x 4 root root   2048 Oct  1 06:58 .
drwxr-xr-x 4 root root  16384 Jan  1  1970 ..
drwxr-xr-x 2 root root   2048 Oct  1 06:58 archiso
drwxr-xr-x 2 root root   2048 Oct  1 06:58 boot
-rwxr-xr-x 1 root root 771136 Oct  1 06:58 shellx64_v1.efi
-rwxr-xr-x 1 root root 893184 Oct  1 06:58 shellx64_v2.efi

# df
...
/dev/sdb1         585728  585728         0 100% /mnt
/dev/sdb2          31662   26104      5558  83% /media

Question:
I dd-ed an iso file (it is a bit-for-bit copy/cloning), which resulted in
sdb1.
What is this sdb2 about, where did it come from ?

I see the above happen with Arch Linux iso, but not with Fedora iso:
# lsblk 
...
sdb      8:16   1  3.8G  0 disk 
└─sdb1   8:17   1  598M  0 part 
...
# lsblk -f
...
sdb    iso9660 Fedora-Live-LXDE-i686-20-1
                                2013-12-12-03-47-50-00               
└─sdb1 iso9660 Fedora-Live-LXDE-i686-20-1
                                2013-12-12-03-47-50-00               
...

jb