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Solution: dd too slow on Mac OS X

Published 2013/10/09 by Daoyuan Li

When I was cloning SD cards on Mac OS X using `dd’, it takes ages to get things done. I was using the following command:

diskutil unmountDisk /dev/disk2
sudo dd bs=1m if=~/Downloads/2013-10-09.alice.img of=/dev/disk2

It takes much less time when using /dev/rdisk2 instead of /dev/disk2:

diskutil unmountDisk /dev/disk2
sudo dd bs=1m if=~/Downloads/2013-10-09.alice.img of=/dev/rdisk2

The reason is that rdisks are “raw” thus resulting in a higher R/W speed, according to `man hdiutil` [1]:

/dev/rdisk nodes are character-special devices, but are “raw” in the BSD sense and force block-aligned I/O. They are closer to the physical disk than the buffer cache. /dev/disk nodes, on the other hand, are buffered block-special devices and are used primarily by the kernel’s filesystem code.

[1] http://superuser.com/questions/631592/mac-osx-why-is-dev-rdisk-20-times-faster-than-dev-disk

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58 Comments

  1. Greg Spenipp

    Incredible! Been banging my head on this for a couple hours now, thanks a bunch!

    2018/12/15 Reply
  2. Darkcaster

    Nice … always a good thing to know 😉 … and a lot of comments helps more =)

     

    Thx you all !

    2018/03/01 Reply
  3. Anonymous

    Life saver!

    2018/02/15 Reply
  4. Tim

    I’m dying from the slowness as well, but using the r trick isn’t working for me. I get the following error:

    dd: /dev/rdisk4: Invalid argument

    Any idea how to fix that?

    2018/02/11 Reply
  5. Mario

    Instead of pv or any other commands you could simply use ‘CTRL + T’ to get the bytes progress.

    2018/02/03 Reply
  6. Mikhail

    Thanks a lot!

    Another tip for OSX (High Sierra) to check status during the process (pv not installed).

    In another Terminal window:

    sudo kill -INFO $(pgrep ^dd)

     

    2018/02/03 Reply
  7. thank you

    818+0 records in
    818+0 records out
    857735168 bytes transferred in 75.526248 secs (11356782 bytes/sec)

     

    2018/01/06 Reply
  8. parabolan

    legendary pro tip, much appreciated

    2017/12/16 Reply
  9. Dixon Dick

    Thank you! Four years later, still a useful tip.

    2017/12/11 Reply
  10. runeb

    Thanks for the tune-up! Much appreciated advice. 20x increase in performance. By prepending an ‘r’. Who knew…

    2017/11/14 Reply
  11. Chris sms

    3299514 bytes/sec
    vs
    15451963 bytes/sec
     

    Thanks a lot! 🙂

    2017/11/12 Reply
  12. davembg

    bail(){
    echo “Usage: $0 source destination”
    exit 1
    }

    nofile(){
    echo “Usage: $0 source destination – path invalid”
    exit 1
    }

    [[ -z “$1” || -z “$2” ]] && bail
    [[ ! -e “$1” || ! -e “$2” ]] && nofile

    read -p “Are you sure? Y/[N] ” -n 1 -r
    echo # (optional) move to a new line
    [[ ! $REPLY =~ ^[Yy]$ ]] && exit 1

    BLKSZ=1048576
    FSZE=$(stat -f “%z” $1)
    su root -c “dd bs=$BLKSZ if=$1 | pv -s $FSZE | sudo dd of=$2 bs=$BLKSZ”

    2017/11/11 Reply
  15. balua

    Apple:~ apple$ sudo dd if=/Users/apple/Desktop/2017-07-05-raspbian-jessie-lite.img of=/dev/rdisk1 bs=1048576
    Password:
    load: 0.59 cmd: dd 1621 uninterruptible 0.00u 0.92s
    1130+0 records in
    1129+0 records out
    1183842304 bytes transferred in 2143.597669 secs (552269 bytes/sec)

    size of jessie -> 1,72,56,29,563 bytes (1.73 GB on disk)

    2017/09/22 Reply
  16. Dill

    Big hug !

    2017/09/10 Reply
  18. Anonymous

    Thank you!

    2017/06/23 Reply
  19. Dave

    Wow. That one character makes a HUGE difference. My DD job went from 3 hours to 5 minutes. Thank you!

    2017/05/09 Reply
  22. Salvatore Restuccia

    Amazing!! 84MB/S Thank you!!!!!

     

    2017/02/13 Reply
  23. Anonymous

    Thank you very much, it works like a charm!

    2017/02/08 Reply
  24. Ken H.

    Nm, I just found out what I did wrong.  I realized that my sd card changed to disk6 instead of disk5.  Doh

    2017/02/06 Reply
  25. Ken H.

    Sorry for the newbie question, but I keep getting a “dd: /dev/rdisk5: Operation not permitted”  when I enter “sudo dd bs=1m if=/Users/me/Desktop/file.img of=/dev/rdisk5”  Not sure what I’m doing wrong.

    2017/02/06 Reply
  26. Rainer S.

    Bonus: for those who use pv for getting a progress meter:
    Use dd from gnu coreutils (both macports and homebrew should have it) and then append

    status=progress

    to your command.

    2017/01/26 Reply
  27. Brian

    Wohoo!!  45MB/s!!!  Thanks!

    2016/11/17 Reply
  29. Name

    Soooo much better – thanks!

    2016/10/08 Reply
  30. Big data

    谢谢分享！

    2016/09/07 Reply
  31. Jon

    Holy Crap!

    Sustained io writes @ 7mb/s!!

    Thank you!!!

    2016/08/19 Reply
  32. darkfader

    Same for databases (like 50%+ faster running off raw devices) but rarely used there because there’s too high chance junior sysadmins / devs will confuse your database storage for empty disks 🙁

    2016/08/07 Reply
  33. John Doe

    Damn I read this too late, now I won’t kill the process because the whole image is “only” 3,3 GB:

    sudo killall -INFO dd

    2459+0 records in
    2458+0 records out
    2577399808 bytes transferred in 5596.141697 secs (460567 bytes/sec)

     

    2016/08/05 Reply
  35. Shane

    AWESOME! You just made my day with this.

    2016/06/21 Reply
  36. Petersen

    Xie xie hen hao!!

     

    2016/05/25 Reply
  37. jdoubleu

    Thanks a lot !!
    Here with pv command to see the copy progress ?
    dd bs=1m if=~/Downloads/2013–10–09.alice.img | pv | sudo dd bs=1m of=/dev/rdisk2

    I’d use:
    sudo -s — “dd bs=1m if=imagefile.img | pv | dd bs=1m of=/dev/rdisk2”
    Because you have to run dd with root privileges.

    2016/04/26 Reply
  38. Kamal

    What a great Tip

    2016/04/23 Reply
  39. Mark

    WOW, this made all the difference it the world!! add the pv command (not needed as much now due to how fast it is) and I can get back to work.

    2016/04/08 Reply
  40. Anonymous

    Amazing.. I was spending hours and it was killing me

    2016/03/14 Reply
  41. Anonymous

    Thanks a lot !!
    Here with pv command to see the copy progress 😉
    dd bs=1m if=~/Downloads/2013–10–09.alice.img | pv | sudo dd bs=1m of=/dev/rdisk2

    2016/02/08 Reply
  42. Anonymous

    Thanks a lot man!!! You saved my life!!!!

    I have a fast external disk that I want to backup to the local MAC disk and an USB 3.0 SATA adapter and got only 30 Mbytes/s.

    Now is 300Mbytes/s!!!!!

     

    Thanks!!!!

    Thanks!!!!

    Thanks!!!

    2016/02/06 Reply
  43. Christophe Nouvel

    So I can keep my Mac and don’t throw it away! Thanks a LOT, x16 speed on a USB stick!

     

    2016/01/25 Reply
  44. Anonymous

    This is huge! Thanks!

    2016/01/20 Reply
  45. test

    thanks

    2015/12/17 Reply
  46. Eik

    Thanks man. You prolonged my life 😉

    2015/12/08 Reply
  47. Jeffrey

    Thank you very mutch saved me mutch time 🙂

    2015/10/23 Reply
  48. Paul

    You Sir, just made my day. This clever trick just speed up dd from 1MB/s to almost 7MB/s

    2015/07/12 Reply
  49. Skippy

    I have been looking for a way to do this for ages 😀

    2015/04/10 Reply
  50. Stuart

    I think I love you. Thank you so much for this!

    2015/03/10 Reply
  51. jsquaredz

    Great tip.  Thanks.  Amazing speed increase.

    2015/03/08 Reply
  52. fred

    Thnx !!

    After more then 10 hours writing to a sd cancelled it,

    Now done in a couple of minutes

    2015/02/20 Reply
  53. Joern

    3284139520 bytes transferred in 19705.137328 secs (166664 bytes/sec)

    vs

    3284139520 bytes transferred in 255.784407 secs (12839483 bytes/sec)

     

    Thanx! 🙂

    2014/12/29 Reply
  54. Waldemar Barbe

    Thank you! 🙂

    2014/10/27 Reply
  56. Gonzo Fialho

    Wow, that improved my life 100%
    Thanks for sharing

    2014/07/20 Reply

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