I am trying to setup a new hard drive into my Macbook Pro. However, I keep getting an error in disk utility that states, "Unable to write to the last block of the device." I saw another person was able to solve this by replacing a dead hd cable. Could someone explain what they meant by dead hd cable, or have any other ideas on how to fix this? Thanks for the help

  • 2
    If it is a new HDD as you say, bring it back and get a new one. You do not want to mess with it by replacing the HDD head cables ect..
    – Ruskes
    Commented Jun 30, 2014 at 19:14
  • I believe he's referring to the HDD's SATA cable. Depending on which model you have will affect how likely the issue could be the cable. Apple found that early versions of their unibody machines started to have issues with the SATA cable, they had to inspect them with x-ray machines to find out.
    – Fyrefly
    Commented Jun 30, 2014 at 19:33
  • @Buscar웃 it ended up being the cabling. My computer is over 4 years old, and after that time the cabling tends to die (according to some mac forums). Commented Jul 15, 2014 at 13:55

2 Answers 2


The HDD cable physically attaches the internal drive (2.5'' 9mm traditionally for notebooks) to the logicboard, typically via the SATA (II or III) bus. The cable can wear out and cause I/O problems, such as you've as described.

Here is an image of the cable via iFixit. I added brief descriptions:

enter image description here

Using iFixit, identify your machine's model and find the applicable replacement guide for the cable (example). In the guide's preface, see "relevant parts" for the compatible cable and necessary tools. Prices range from $30-$50. Follow the step by step guide carefully and replace the cable.

If you still have the same issue after doing so, the drive itself is defective and should be returned.

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    Thanks for the response, I believe this is the issue. My macbook has not been able to read any of my hard drives, even ones that previously worked. I just got back from the apple store and they told me it would cost $50 and take 5 to 7 days to replace. They then told the lady next to me she would have to wait 3 hours for a new battery. I understand they were busy, but to wait a week for a job that can be done in minutes seems ridiculous. Thanks for the link, it will be much cheaper and faster to fix it myself. I'll be sure to accept your answer if it works. Commented Jul 8, 2014 at 20:16
  • I just replaced the cable and everything is working fine. If anyone's mac starts up with a folder and question mark (mac can't find the OS) I would check the cable first. I assumed it was my hard drive, so I immediately bought a replacement. However the 'genius' at the apple store said that the cable being the issue is more common, and from what I read on the internet after four years the cable tends to die. I should have performed the test bmike mentions. This would have just saved me the money and time I spent on the new hard drive. Thanks again for the help. Commented Jul 15, 2014 at 13:51

Testing cabling is more of an empirical exercise. First you disconnect and reseat both ends of the cable. Next, you put in the new cable and if the problem goes away it was the cable. If you suspect the cable on an intermittent problem you replace the cable and leave it in after reseating doesn't reduce the frequency of the issue.

I'd start with reseating things and re-testing. Since you have a good test you'll know pretty quickly if it's the drive, the cable or the driver board / software that's causing the write failure.

Also, check that the drive has updated firmware / appropriate firmware for your version of OS.

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    Ended up being the cabling. Thanks for the help, performing this test would have saved me some money on ordering a new drive. Commented Jul 15, 2014 at 13:52

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