User profile for user: JohnnieLeMaster
JohnnieLeMaster Author
User level: Level 1
4 points

External Time Machine drive inaccessible; erase fails

I was using a 2 TB WD external drive for my Time Machine Backups. I'm on a 2019 MacBook Pro using Sonoma 14.6.1. Now when I plug it in, I can't get it to show up and it can't be accessed. Tried it on another MacBook as well. It's not an encrypted drive. When I go to disk utilities, it's recognized as connected, but when I try to erase it to wipe it slick and start over, I get the following error:


"Erase process has failed. Click Done to continue". and "Unmounting disk, Couldn't open disk. : (-69879)


In Disk Utility, when I run First Aid on the drive, it gets a green check, clean report (as follows):


"Checking prerequisites

Checking the partition list

Checking the partition map size

Checking for an EFI system partition

Checking all HFS data partition loader spaces

Checking booter partitions

Checking Core Storage Physical Volume partitions

The partition map appears to be OK


Operation successful."


I'd rather not buy a new drive if I don't have to. Help! Thanks.


MacBook Pro 16″, macOS 14.6

Posted on Dec 9, 2025 1:59 PM

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User profile for user: Owl-53
Owl-53
User level: Level 10
102,373 points

Posted on Dec 10, 2025 3:19 AM

Fixes for Error -69879: Couldn't open disk

1. Quit any WD software (most common fix)

WD software often locks the drive:

  • WD Discovery
  • WD Utilities
  • WD Security
  • WD Backup
  • WD Drive Unlock.app
  • Paragon / Tuxera NTFS drivers (common with WD drives)

Do this:

  1. Quit all WD apps
  2. Open Activity Monitor and quit any process starting with:
    • WD
    • WesternDigital
    • Paragon
    • Tuxera
  1. Eject and unplug the drive
  2. Plug it in again
  3. Try erasing again (Disk Utility → View → Show All Devices → select top drive → Erase)

Remove WD Virtual CD (if present)

Many WD drives have a locked firmware partition that causes -69879.

Look in Disk Utility → View → Show All Devices.

If you see:

  • WD Unlocker
  • Virtual CD
  • WD Security partition



If present:

Fix:

  1. Open WD Drive Unlock.app (it appears when the drive mounts)
  2. Unlock it if needed
  3. Uninstall WD Discovery / WD Security (this removes the virtual CD)
  4. Reconnect drive
  5. Erase again



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2 replies
Question marked as Top-ranking reply
User profile for user: Owl-53
Owl-53
User level: Level 10
102,373 points

Dec 10, 2025 3:19 AM in response to JohnnieLeMaster

Fixes for Error -69879: Couldn't open disk

1. Quit any WD software (most common fix)

WD software often locks the drive:

  • WD Discovery
  • WD Utilities
  • WD Security
  • WD Backup
  • WD Drive Unlock.app
  • Paragon / Tuxera NTFS drivers (common with WD drives)

Do this:

  1. Quit all WD apps
  2. Open Activity Monitor and quit any process starting with:
    • WD
    • WesternDigital
    • Paragon
    • Tuxera
  1. Eject and unplug the drive
  2. Plug it in again
  3. Try erasing again (Disk Utility → View → Show All Devices → select top drive → Erase)

Remove WD Virtual CD (if present)

Many WD drives have a locked firmware partition that causes -69879.

Look in Disk Utility → View → Show All Devices.

If you see:

  • WD Unlocker
  • Virtual CD
  • WD Security partition



If present:

Fix:

  1. Open WD Drive Unlock.app (it appears when the drive mounts)
  2. Unlock it if needed
  3. Uninstall WD Discovery / WD Security (this removes the virtual CD)
  4. Reconnect drive
  5. Erase again



Reply

External Time Machine drive inaccessible; erase fails

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