Back up external hard drives


You can use the Code42 agent to back up storage connected to your device, such as an external hard drive directly attached via USB, Thunderbolt, or Firewire. By adding the contents of an external drive to your backup file selection, the Code42 agent backs it up just like other files on your device.


This article assumes you have permission to change your backup file selection. Your administrator may prevent editing of the backup file selection.


  1. Attach your external drive to your device.
  2. Open the Code42 agent.
  3. Go to Manage Files
  4. Above the file list, click your device name in the breadcrumb.

Device breadcrumb highlight

  1. To back up the entire drive, select the box to the left of your external hard drive. To select only specific files or folders for backup, click the drive, then browse the contents and select the items you want to back up.
  2. Click Save.
    The Code42 agent begins backing up the files on your external drive.


What happens if I disconnect my drive?

Your backed up files are safe when the drive is disconnected as long as your version setting for deleted files is set to Never (the default setting). When you reconnect the drive, the Code42 agent resumes backup from where it left off. If you reconnect the drive and the Code42 agent doesn't recognize it immediately, it is likely because the drive letter or name changed. See the troubleshooting tips below to correct the issue.


Note: If your external drive isn't connected to your device when the Code42 agent runs the file verification scan, it's possible your backup status will report 100%, even if there are additional files on the drive that need to be backed up. The next time the drive is connected, the Code42 agent will detect the changes and adjust your backup status.

Replace a drive

To add a new drive to replace a drive that you no longer use, add the new drive to the file selection.

Once the new drive is selected, the data on the new drive is de-duplicated against what is stored in the archive. This process is entirely automatic and no action is required on your part. The old path may display as "Missing" while the Code42 agent performs a synchronization (file verification scan). Once the Code42 agent displays that synchronization is complete in the progress bar, you can deselect the old drive's file path.

Best practices (Windows)

When you connect an external drive to a Windows device, the operating system automatically assigns the next available letter in the alphabet. If the letter changes when you reconnect a drive you've been using for backup, the Code42 agent won't recognize the drive. To prevent this recognition error, assign a static drive letter to your external drive.

Troubleshooting tips

Code42 app reports drive as "missing"

This issue occurs when the external drive is disconnected from the device or the letter or name assigned to the drive by your operating system changes. The Code42 agent uses absolute paths when backing up. If the Code42 agent cannot detect a drive at the specified location, such as when it is disconnected or when the name of a drive changes, it lists the drive as "Missing". You can correct the issue by reconnecting the drive or renaming the drive to match the original drive letter or name.

External drive stops backing up (Mac)

If an external drive stops backing up on a Mac, it is likely because the drive didn't unmount cleanly (for example, after a power outage, or disconnection without ejection). When this happens, the drive can leave behind a "ghost" folder in /Volumes, even though the drive is no longer mounted. When the external drive re-mounts to your device, the "ghost" folder name is already taken, so your device adds a “1” to the external drive's name. However, the Code42 agent looks for a folder with the original name, and that folder belongs to a drive that appears to be no longer connected. Use our troubleshooting guide to diagnose and correct this issue.