How To Fix MAC Error VolOnLinErr Drive Volume already on-line at MountVol

Dealing with MAC Error VolOnLinErr can be frustrating, especially when they prevent you from accessing files and drives. The “Fix MAC Error VolOnLinErr Drive volume already on-line at MountVol” error is one such error that you may encounter when trying to mount external drives or volumes on your Mac. Thankfully, there are a few troubleshooting steps you can try to resolve this issue. In this article, we’ll walk through the common causes of this error and the step-by-step solutions to fix it.

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What Causes the “volOnLinErr drive volume already on-line at MountVol” Error?

This error typically occurs when the system attempts to mount a drive or volume that it believes is already mounted. There are a few common reasons why this error may show up:

  • An improper ejection of the external drive: If you don’t properly eject and disconnect the drive before unplugging it, the system still thinks it’s connected. When you try to reconnect it, the “already on-line” error appears.
  • Drive corruption: File system corruption or damaged sectors on the external drive can cause the system to get confused about the drive’s status.
  • Problems with system files: Outdated or corrupted system files associated with mounting drives can also lead to this error.
  • Drive formatting issues: If the drive is formatted using an unsupported file system, that can prevent the system from properly recognizing and mounting the drive.

So in most cases, this error occurs because of disconnects between what the system thinks is happening versus what is actually occurring with the external drive. Thankfully, the solutions typically revolve around resetting those connections.

Step 1: Restart Your Mac

The first troubleshooting step to try is simply restarting your Mac. Rebooting can clear out any false connections and allows a fresh start for recognizing drives and volumes.

Here are the steps to restart your Mac:

  1. Save any open documents and close all applications. This avoids potential data loss.
  2. Click the Apple menu and select “Restart…”
  3. Click the “Restart” button in the confirmation dialog.
  4. Allow your Mac to fully shut down and wait at least 30 seconds before powering back on.

Once restarted, try to mount the drive again and see if the error has resolved. If the error still appears after a restart, move on to further troubleshooting steps.

Step 2: Repair Disk Errors Using Disk Utility

If a restart doesn’t fix the problem, the next step is using Disk Utility to check for errors and repair the drive. Disk errors can often cause this type of mount error, so verifying and fixing the disk is key.

To use Disk Utility:

  1. Open Disk Utility (located in Applications > Utilities).
  2. Select the external drive that is showing the error from the left sidebar.
  3. Click “First Aid” at the top of the Disk Utility window.
  4. Click “Run” to begin checking for errors and problems.
  5. Allow Disk Utility to fully check and repair the disk. This may take some time.
  6. When finished, eject the disk properly then disconnect it.
  7. Reconnect the disk and see if you can now mount it without the error.

Running First Aid will check the disk for file system errors, directory issues, or bad sectors, then attempt repairs. This should resolve any underlying drive issues leading to the mount error.

Step 3: Unmount and Remount the Drive

If drive repair doesn’t resolve the issue, trying unmounting then remounting the drive may reset the connection.

To do this:

  1. Open Disk Utility and select the external drive.
  2. Click “Unmount” at the top of the window.
  3. After the drive unmounts, disconnect it from your Mac.
  4. Reconnect the drive to your Mac.
  5. Go back to Disk Utility and select the external drive.
  6. Click “Mount” to remount the drive.

This essentially ejects the drive fully on a system level, clearing out any false remnants of a connection. Remounting it then allows a fresh start. Check if the “already on-line” error still appears after remounting the drive.

Step 4: Reset the SMC on Your Mac

Resetting the System Management Controller (SMC) can help resolve system errors, including issues mounting drives. Here are the steps to reset the SMC:

For Mac notebooks:

  1. Fully shut down your Mac.
  2. Keep the power cable plugged in.
  3. Press and hold the left Shift, Option, and Control keys and the power button simultaneously for 10 seconds.
  4. Release all keys.
  5. Power your Mac back on and test the drive.

For Mac desktops:

  1. Shut down your Mac and unplug the power cable.
  2. Press and hold the power button for 10 seconds.
  3. Reconnect the power cable and power on your Mac.
  4. Test to see if the error still occurs when mounting the drive.

Resetting the SMC resets the connections between the Mac’s motherboard and components like drives. This often resolves mount issues like this error.

Step 5: Seek Further Assistance

If all the above steps fail to resolve the MAC Error VolOnLinErr, you will likely need to seek additional help. Some further things to try include:

  • Contact Apple support for assistance, especially if repairing the disk does not work.
  • Take your Mac and the affected drive to an Apple store for troubleshooting.
  • Use a third party data recovery service if critical files are inaccessible on the drive with the error.
  • Consult with an IT professional or technician if you cannot fix the issue on your own.

While frustrating, this error is typically resolvable with one of the troubleshooting steps outlined above. Just try each solution one at a time until the error is cleared and you can once again access the external drive.

Helpful Table for Troubleshooting the “volOnLinErr” Error

<table> <thead> <tr> <th>Troubleshooting Step</th> <th>How To Do It</th> </tr> </thead> <tbody> <tr> <td>Restart your Mac</td> <td>- Fully shut down your Mac<br>- Wait at least 30 seconds<br>- Power back on and retest drive</td> </tr> <tr> <td>Repair disk errors</td> <td>- Open Disk Utility<br>- Select drive and click “First Aid”<br>- Click “Run” and allow repairs</td> </tr> <tr> <td>Unmount then remount</td> <td>- Unmount drive in Disk Utility<br>- Disconnect then reconnect drive <br>- Remount drive</td> </tr> <tr> <td>Reset SMC</td> <td>- Shutdown Mac and unplug (desktop)<br>- Hold power 10 secs (desktop)<br>- Hold Shift+Option+Control+Power 10 secs (notebook)</td> </tr> <tr> <td>Seek further help</td> <td>- Contact Apple support<br>- Visit Genius Bar<br>- Use data recovery service<br>- Consult technician</td> </tr> </tbody> </table>


The “volOnLinErr drive volume already on-line at MountVol” error ultimately means your Mac is having trouble mounting and connecting to an external drive. While frustrating, this issue can typically be resolved through troubleshooting steps like restarting, repairing disk errors, resetting drive connections, or resetting low-level system management controls. Check each solution in a systematic order until the error is cleared. Seek additional assistance if needed. With the right steps, you should be able to regain access to your important external drives.

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