I can't access my TOSHIBA External USB 3.0 Media external hard drive. Now I'm trying to format it but I get this error message:

Erasing "TOSHIBA External USB 3.0 Media" (disk3) and creating "Untitled"

Unmounting disk
Creating the partition map
Unable to write to the last block of the device.: (-69760)
The operation failed ...

How can I resolve this issue?


1 Answer 1


I've run across this a few times before and there were two approaches that worked:

  • Format the drive in a Windows machine (FAT32 or NTFS is fine)
  • Zero out the drive. This, in effect, writes zeros on every single datablock on your hard/solid disk drive.

    % sudo dd if=/dev/zero of=/dev/diskN bs=8m     ← Where diskN is your disk identifier

The idea is to write each block with a zero overwriting whatever was there corrupting it. Keep in mind, this will take a long, long time so if you have a Windows machine handy, it makes sense to first format it there then try again in macOS.

  • Toshiba sells only one external SSD (in Germany): Toshiba XS700 960GB, USB-C 3.1. All other external drives (64 available in Germany) are HDDs... ;-)
    – klanomath
    Commented Apr 14, 2020 at 22:59

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