Occasionally a backup task can stall if the source or destination stops responding. To avoid waiting indefinitely for a filesystem to start responding again, Carbon Copy Cloner has a "watchdog" mechanism that it uses to determine if its file copying utility has encountered such a stall. By default, CCC imposes a ten minute timeout on this utility. If ten minutes pass without hearing from the file copying utility, CCC will collect some diagnostics information, then stop the backup task. Our support team can analyze this diagnostic information to determine what led to the stall.
Common factors that lead to stalls
Hardware problems are the most common cause of a stall. There are a few other factors that can lead to a stall, though, depending on how the backup task is configured:
- Filesystem corruption or media problems on the source or destination can prevent that filesystem from providing a file or folder's filesystem entry
- A firmware problem in an external hard drive enclosure can cause that device to stop responding
- File sharing service errors can lead a network volume to become unresponsive
- Access to a network volume via a wireless connection may become slow enough that the volume stops responding
- Excessive bandwidth competition from other software can cause a volume to appear unresponsive, though it may just be responding very slowly
The first thing you should do if a task ends with this result is to reboot your Mac and run the task again. In many cases, an unresponsive filesystem is a transient problem, and the simple act of restarting will get the volume remounted in a better state. If the problem recurs, please choose Report a problem from CCC's Help menu and our support team can offer more specific troubleshooting suggestions. Below is a list of some of the troubleshooting suggestions we may offer depending on how your task is configured.
- Use Disk Utility's First Aid tool to check for any filesystem problems on the source volume. If any are discovered and the source is your startup disk, reboot while holding down Command+R to boot from the Recovery volume, then use Disk Utility to repair the problems. Please note: A report of "No problems found" from Disk Utility does not mean that there are no problems with that volume. There are no hardware diagnostic utilities on the market that will inform you of a problem with a cable, port, or enclosure, or report a bug in the firmware of a hard drive or SSD.
- Exclude a file or folder from the backup task. Select Selected files... from the Clone popup menu (underneath the Source selector), then uncheck the box next to the item that the source filesystem is unable to read.
- Remove a corrupted item from the destination volume.
- Erase the destination volume (we make this recommendation sparingly, and only when the stall can be definitively identified as a filesystem problem on the destination).
- Disable Spotlight on the destination volume to reduce bandwidth competition. To disable Spotlight, open the Spotlight preference pane, click on the Privacy tab, then drag the backup volume into the Privacy table. This only affects the destination volume, and it's reversible, you can remove it from that list should you decide that you want to re-enable indexing.
- If the stalling volume is a network volume, connect your Mac and the host of the network volume to the network via a wired connection (i.e. rather than via a wireless connection, if applicable).
- If the stalling volume is a network volume, eject that volume in the Finder, then remount the volume using a different file sharing protocol.