macOS Sierra : dd to USB is very slow and can't seem to use /dev/rdisk (txs all for your help and suggestions, but suspending this for now while I track down my formatting errors on that SD.  If I can't get that to work, little reason to expect dd to work, even if other people have encountered similar issues doing this on osx).

I'm trying, as root, to write to micro SD to load up a Raspberry Pi's Linux:

W$dd bs=1m if=/Users/jluc/Downloads/2017-01-11-raspbian-jessie.img of=/dev/disk2

This is supremely slow, it's been running for 8-9 hours and hasn't written much when I kill -9 it.

301989888 bytes transferred in 23103.442503 secs (13071 bytes/sec)

Now, in such write ups as Solution: dd too slow on Mac OS X, he advises to use /dev/rdisk, because it's treated differently.

But every time I've used /rdiskN instead of /diskN, I get:  

dd: /dev/rdisk2: Input/output error

This is on Sierra, but it worked on Yosemite, if I recall correctly.

INSTALLING OPERATING SYSTEM IMAGES ON MAC OS mentions the possibility that /rdisk won't work and advises you to use /disk instead.

What gives?  Is this something new with Sierra as opposed to earlier versions?

update:  tried suggestion as per @oa and still getting the same error.

Searching `` got me this:  https://stackoverflow.com/questions/37232109/how-to-fix-bad-dd-img-write-to-sdcard.  Now, that post is about an img file that is too big for the SD.  I have a 4.1Gb img, and this is a 32Gb file, so that wouldn't apply.

But... what I've noticed is that diskutil list has a number of things for that disk.

jluc@node_modules$ diskutil list /dev/disk2
/dev/disk2 (external, physical):
#:                       TYPE NAME                    SIZE         IDENTIFIER
 0:     FDisk_partition_scheme                        *32.1 GB    disk2
 1:             Windows_FAT_32 boot                    66.1 MB    disk2s1
 2:                      Linux                         32.0 GB    disk2s2


See how the first partition, the FAT32 boot shows @ 66.MB?

Looking some more:

jluc@node_modules$ df -h | egrep "disk2|Filesystem"
Filesystem                          Size   Used  Avail Capacity iused      ifree %iused  Mounted on
 /dev/disk2s1                        63Mi   21Mi   42Mi    33%     512          0  100%   /Volumes/boot


So, wondering if it's not that /dev/disk2 is not interpreted as being only 60 MB because of the boot and I am therefore getting a capacity error.  Will try to repartition it first.
I installed the same image last night on a RPi3.

You need to unmount the disk first. Then you can write to the disk using sudo. 

diskutil unmountDisk /dev/rdisk2
sudo dd bs=1m if=~/Downloads/your_image.img of=/dev/rdisk2
diskutil unmountDisk /dev/disk2


I'm on macOS Sierra, too.