dd command finished very quickly but does not transfer data I'm trying to restore a Windows installer image to an external hard drive. To do this, I decided to use the command line because Disk Utility never bloody works. 

To identify the disk, I used diskutil list which generated the following output:

$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage Macintosh HD            499.4 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

/dev/disk1 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            Macintosh HD           +499.0 GB   disk1
                                 Logical Volume on disk0s2
                                 604D1BA8-46A5-41AD-8D62-7898021A4D16
                                 Unencrypted

/dev/disk3 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:                  Apple_HFS 500G Storage            489.8 GB   disk3s2
   3:       Microsoft Basic Data WINDOWS                 9.9 GB     disk3s3


I identified the disk I want to use as disk3s3, a 10GB MS-FAT partition on the external hard drive. I then unmounted it with sudo diskutil unmount /dev/disk3s3. Now, to restore an ISO image to this partition, I use the following command:

$ sudo dd if=~/Desktop/Windows.iso of=~/dev/disk3s3 bs=1m

I don't get any errors upon running the command initially but after only a few seconds it finishes with this output:

3165+1 records in
3165+1 records out
3319764992 bytes transferred in 10.191605 secs (325735246 bytes/sec)


However much I wished this output was correct, it is not. No data whatsoever was transferred to the drive. How is this possible?

Thanks in advance
Everything is OK except that you shouldn't use ~ in dd commands (it's not forbidden but error-prone) and of=~/dev/disk3s3 is a file in your /Users/yourusername/dev folder (which probably wasn't intended but explains the 326 MB/s) instead of the real destination /dev/disk3s3.

So better enter:

sudo dd if=~/Desktop/Windows.iso of=/dev/disk3s3 bs=1m


or much better

sudo dd if=/Users/yourusername/Desktop/Windows.iso of=/dev/disk3s3 bs=1m