Carbon Copy Cloner
Knowledge Base > Carbon Copy Cloner 3.5

“CCC found multiple volumes with the same Universally Unique Identifier”

This documentation is for an older version of CCC. This article has been retired, so it does not exist in the knowledge base for the newest version.
Last updated on 16 juli 2014

Occasionally a circumstance arises in which CCC presents the following error message before creating or running a scheduled backup task:

CCC found multiple volumes with the same Universally Unique Identifier that was associated with the volume you designated as the source for this task.

CCC cannot proceed with confidence in having correctly identified the volume you originally chose when you configured this backup task. Unmount one of the conflicting volumes and try the task again, or please choose "Ask a question" from CCC's Help menu to get help resolving the issue.

Most modern operating systems apply a universally unique identifier to a new volume when you format that volume (e.g. in Disk Utility). Volumes should never have the same identifier, these identifiers are called "universally unique" because they're suppose to be unique, universally! Wikipedia notes that, for 122 bit UUIDs, there is a 50/50 chance of having a single duplicate UUID if 600 million UUIDs were allocated to every person on Earth. The chances of two volumes having the same UUID should, then be slim enough that the UUID can be reliably used to positively identify the source and destination volumes.

Given these odds, it is statistically more likely that CCC's discovery of a duplicate UUID is due to a hardware or software problem rather than to two volumes randomly having the same UUID. Therefore, CCC makes the conservative decision to not back up to either volume if another volume with the same UUID is detected.

Unfortunately, it has come to our attention that many Iomega drives that are pre-formatted for OS X are stamped with the same UUID at the factory (BDFE6D09-7483-3479-B37F-0BE15F9CBFBB). As a result, this situation can arise if you own and attach two "factory fresh" Iomega hard drives to your computer.

There are two solutions to this problem:

  1. Reformat one of the affected volumes in Disk Utility. A new UUID is generated every time you reformat a volume.
  2. In the Settings tab in the scheduler window, you can uncheck the box that indicates CCC should use "Strict volume identification"

To determine the identity of the two affected volumes, choose "CCC Log" from CCC's Window menu.

Update: Western Digital also ships 3TB hard drives with the same "unique" identifier, "5ADAD698-026F-3970-9245-A05DDE814C78". If you have two new hard drives from Western Digital, simply reformat one of the disks to give it a new, truly unique identifier before using it for backup purposes.