Solved: Unable To Write to the Last Block of the Device

  • This error message can come up when attempting to partition an external or internal drive.
  • Disk Utility is going to be quite helpful for several of these solutions.
  • If you continue to experience issues, you may want to contact Apple Support.

Looking to fix Unable To Write to the Last Block of the Device error on your Mac? This error can often say something like Unable To Write to the Last Block of the Device (-69760) external. Whether you are receiving this while partitioning an internal drive or even an external drive, I can show you solutions that may help your problem. However, it may just be time to replace the entire disk. Let’s take a look. 

How To Fix Unable to Write to the Last Block of the Device

Before we take a look at more advanced solutions, try some of these suggestions:

  • If you’re using an external drive, try replacing the cables. It may also be a problem with your internal connection or a communication issue causing the error.
  • If you are attempting to erase the disk drive via Disk Utility (full guide here), you may want to try erasing it multiple times. Disk Utility may not always wipe the drive the first time, so another attempt may be just the trick.
  • While you may want to try the solutions below, swapping your SATA Cable or Controller may solve your issue. A bad drive cable may cause a connection issue. You can also take out your SSD from your Mac and test it via an external enclosure to see if you have a bad drive.
  • If the drive is behaving poorly, it may be time to swap it out for a new one.

1. Using Internet Recovery Mode to Erase Drive (Intel Only)

Note icon NOTE
This only works for Intel-based Macs. You can check your processor by going to Apple > About This Mac from the Menu Bar. If says Intel anywhere under your processor, you are using an Intel-based Mac.

If you are having trouble erasing the drive via Disk Utility, you can attempt to erase the drive via Internet Recovery. This tool uses recovery instruments from Apple servers, allowing you to set up the most current version of macOS supported by your system

Time needed: 1 hour

Follow these steps to use Internet Recovery mode: 

  1. Power down your Mac.

  2. Press the Power button, then immediately press and hold Option + Command + R. Let go of the keys once you see a spinning globe.

  3. Select Disk Utility from the macOS Utilities section.

    Fix Unable To Write to the Last Block of the Device Disk Utility Continue

  4. Choose View and then Show All Devices.

  5. Choose your startup disk (usually named Macintosh HD) and then choose Erase.

    Fix Unable To Write to the Last Block of the Device Disk Utility Erase

  6. Pick a name for your startup disk.

  7. If you are using macOS 10.13 or higher, select APFS for format.

  8. For Scheme, configure it as GUID Partition Map.

  9. Click Erase.

Should the issue persist and you continue to encounter the Unable To Write to Last Block of the Device error, continue to the next solution.

2. Erase the Drive Via External Bootable Installer

Note icon NOTE
This method requires a USB flash drive with 14GB of free space.

You also have the option of using Disk Utility after you load from a bootable installer. Should Recovery Mode not be successful, you can try this method.

  1. Create a bootable USB installer. You can follow our full guide here.
  2. Make sure there is a connection between your USB installer and your Mac.
  3. Ensure you have an internet connection.
  4. Power down your Mac and then detach external devices save for the power cord and installer.
  5. You will then boot from the installer.
    • On Intel Macs: Power on your Mac. Then, immediately press and hold the Option key. Release the key when you see the bootable volumes. Select your installer and then click the up arrow to continue.
    • On Apple silicon Mac: Press and hold the Power buttons until you see the bootable volumes. Then, select your installer and click Continue.
  6. Choose Disk Utility and click Continue.
  7. You will then follow the instructions from the previous method. Start at step three.

What Does Unable To Write to the Last Block of the Device Mean?

If you are receiving an Unable To Write to the Last Block of the Device error, it is likely that your drive is defective. You will more than likely need to replace the drive, especially if your machine is unable to recognize it. However, you can try things such as using Disk Utility, Internet Recovery or a bootable installer to try and fix the drive. You may also want to talk to Apple Support.


While this error message is likely to create a bad experience, there are things you can do to mitigate the damage. A bad drive is going to prevent you from doing virtually anything on your Mac, so be sure to create regular backups often. In this instance, a clean scrub using the above methods should hopefully do the trick if you are getting bad requests or are having an issue with your entire drive. 

If there’s anything you would like to suggest, feel free to let us know in the comments. 

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