Problem copying SD card with `dd` on OSX

Question

i am trying to back up my sd-card(16GB) with Mac using:
sudo dd if=/dev/rdisk3 of=~/Desktop/raspberrypi20161117_r.dmg bs=1m

Output:
dd: /dev/rdisk3: Input/output error 2996+0 records in 2996+0 records out 3141533696 bytes transferred in 170.479861 secs (18427594 bytes/sec)

The Input/output error always comes when 3141533696 bytes transferred.

dd output with /dev/disk3

Outupt:
dd: /dev/disk3: Device not configured 2996+0 records in 2996+0 records out 3141533696 bytes transferred in 1507.614168 secs (2083778 bytes/sec)

The sd-card still works with raspberry pi...

I hope someone can help me to backup the sd card

Thanks

Answer 1

You could try ddrescue or fsck on the Pi (this should run by default if the OS detects an error, but can be manually run).

However I would recommend you get a new SD card, mount it on the Pi in a card reader and use the SD Copy utility in Raspbian to copy to the new card. This actually does a file copy (using rsync) so should recover all the readable files. You may lose a file or so, but it is quite likely the card error is on a part of the file which is unused.