I run out of memory (8GB) in one system, and I need to move the existing system to bigger memory (16GB). 
Details

* /dev/disk4s1 is the input i.e. from where I want to get the data
* /dev/disk2s1 is the sd-card where I want write

I unmount disk2s1, and run

```
sudo dd bs=1m if=/dev/disk4s1 of=/dev/disk2s1

```

but I get

```
dd: /dev/disk4s1: Resource busy

```

I unmount also /dev/disk2s1 but I get `dd: /dev/disk4s1: No such file or directory`. So I should not unmount the input. 

Keeping both SD-cards unmounted, I run XtrmJosh's proposal `sudo dd if=/dev/disk4s1 of=/dev/disk2s1` but get `dd: /dev/disk4s1: No such file or directory`. 

System report of OSX (Sorry, my Ubuntu is upgrading slowly itself now) where I am uncertain if I `dd`ing right things. 
Command `sudo dd if=/dev/disk4s2 of=/dev/disk2s1` is not correct also. 

```
USB 3.0 Bus:

  Capacity: 8,02 GB (8 017 412 096 bytes)
  Removable Media:  Yes
  BSD Name: disk4
  Partition Map Type:   MBR (Master Boot Record)
  PCI Device ID:    0x9c31 
  PCI Revision ID:  0x0004 
  PCI Vendor ID:    0x8086 
  Volumes:
boot:
  Capacity: 62,9 MB (62 914 560 bytes)
  Available:    42 MB (41 951 232 bytes)
  Writable: Yes
  File System:  MS-DOS FAT16
  BSD Name: disk4s1
  Mount Point:  /Volumes/boot
  Content:  Windows_FAT_32
  Volume UUID:  B39523D8-BEFC-3910-95CD-08A0C8F472AF
disk4s2:
  Capacity: 3,96 GB (3 962 568 704 bytes)
  BSD Name: disk4s2
  Content:  Linux

Card Reader:

  ...
  Current Available (mA):   1800
  Current Required (mA):    224
  Extra Operating Current (mA): 0
  Capacity: 15,93 GB (15 931 539 456 bytes)
  Removable Media:  Yes
  Detachable Drive: Yes
  BSD Name: disk2
  Built-In: Yes
  Partition Map Type:   MBR (Master Boot Record)
  Volumes:
NO NAME:
  Capacity: 1,98 GB (1 975 546 368 bytes)
  Available:    1,97 GB (1 972 600 832 bytes)
  Writable: Yes
  File System:  MS-DOS FAT16
  BSD Name: disk2s1
  Mount Point:  /Volumes/NO NAME
  Content:  DOS_FAT_16
  Volume UUID:  2AE73D94-DEE9-3B80-A4DA-0AF2B6449863

Mass Storage Device:

  Product ID:   0x125c
  Vendor ID:    0x14cd  (MOAI ELECTRONICS CORPORATION)
  Version:  3.00
  Serial Number:    125C20100726
  Speed:    Up to 480 Mb/sec
  Manufacturer: Generic
  Location ID:  0x14200000 / 11
  Current Available (mA):   1000
  Current Required (mA):    248
  Extra Operating Current (mA): 0
  Capacity: 8,02 GB (8 017 412 096 bytes)
  Removable Media:  Yes
  Detachable Drive: Yes
  BSD Name: disk4
  Partition Map Type:   MBR (Master Boot Record)
  Volumes:
boot:
  Capacity: 62,9 MB (62 914 560 bytes)
  Available:    42 MB (41 951 232 bytes)
  Writable: Yes
  File System:  MS-DOS FAT16
  BSD Name: disk4s1
  Mount Point:  /Volumes/boot
  Content:  Windows_FAT_32
  Volume UUID:  B39523D8-BEFC-3910-95CD-08A0C8F472AF
disk4s2:
  Capacity: 3,96 GB (3 962 568 704 bytes)
  BSD Name: disk4s2
  Content:  Linux

```

---

How can you dd from smaller SD-card to Bigger?