Carbon Copy Cloner Icon   

"Verification of the target volume failed"

 

When Carbon Copy Cloner performs a block-level clone of your source volume to your target volume, it proceeds in two stages: the cloning stage and the verification stage. Before it begins, both the source and target are unmounted to prevent any external modifications to each filesystem. During the cloning stage, blocks are read from the source volume and written to the target volume. While blocks are read from the source volume, a checksum of those blocks is calculated. In the verification stage, the blocks that were written to the target are now read back and another checksum is calculated. The target volume's checksum is then compared to the source volume's checksum. If these two values do not match, CCC will display an error message that "Verification of the target volume failed".

Verification errors are occasionally the result of errors in hard drive drivers, defective hard drives, or defective cables, hard drive enclosures, etc. Typically, though, verification errors are a result of the failure of one or more sectors of media on the target volume. Many people have seen the result of a failed sector, or "bad block", when they try to access a file and the computer reports that it is unable to read that file. Indeed, bad sectors are not discovered during a write operation, they are discovered during a read operation. When bad sectors are discovered during the verification stage of a block-level clone, Mac OS X marks those sectors as unusable. The next time an application tries to write to an area of the disk that includes the bad sector, the disk firmware will recognize that the sector has been marked as unusable and will write to another sector instead.

Try it again, once

Because this bad sector remapping occurs automatically, there is a very good chance that another block-level clone to the same target volume will work just fine. If you see this kind of error more than once for the same target volume, though, it is possible that there are other problems at play. If that is the case, we recommend substituting another hard drive for the target volume. Apple's Hardware Diagnostics tests can also be very helpful in identifying hardware trouble when encountering multiple verification failures.