You can use CrashPlan to back up storage connected to your computer, 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, CrashPlan backs it up just like other files on your computer.
Follow these instructions to back up files stored on an external drive to another destination, such as CrashPlan Central or another computer.
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, CrashPlan resumes backup from where it left off. If you reconnect the drive and CrashPlan 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 computer when CrashPlan runs the file verification scan, it's possible that your backup status will report 100%, even if there are additional files on the drive that need to be backed up. CrashPlan will detect the changes and adjust your backup status the next time the drive is connected.
When you connect an external drive to a Windows computer, 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, CrashPlan won't recognize the drive. Consequently, we recommend assigning a static drive letter to your external drive.
This issue occurs when the external drive is disconnected from the computer or the letter or name assigned to the drive by your operating system changes. CrashPlan uses absolute paths when backing up. If the CrashPlan app 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.
If an external drive stops backing up on OS X, it is likely because the drive didn't cleanly unmount (for example, after a power outage, or disconnection without ejection, etc.). When this happens, the drive can leave behind a "ghost" folder in /Volumes, even though the drive is no longer mounted. When the drive re-mounts, your computer detects that the folder name for the drive is taken, and consequently appends a “1” to the drive name. However, CrashPlan looks for the folder with the original name, which is no longer connected. Use our troubleshooting guide to diagnose and correct the issue.