Several Network Attached Storage (NAS) devices offer poor performance for reading extended attributes from files on the NAS volume (e.g. when copying those files from the NAS, or when reading existing files on the NAS to determine if they are up to date). This performance problem is independent of CCC, other non-CCC users have reported this on Synology's forums, for example. We have identified a couple workarounds that can avoid the performance problem.
Eject the network volume in the Finder
Our first recommendation is to eject your network shares in the Finder, then run your task again. We have run several tests and positively identified an issue in which the Finder will make repeated and ceaseless access attempts to the items of a folder on your network share if you simply open the network volume in the Finder. This persists even after closing the window. This is a Finder bug, and it exists in both Mavericks, Yosemite, and El Capitan. If you eject the network volume(s), then run your CCC backup tasks, CCC will mount the network volume privately such that it is not browseable in the Finder.
Disable support for extended attributes
If the stall persists despite trying the first workaround, you can try dropping the extended attributes from the source. While it is our preference to preserve extended attributes, Apple considers extended attributes to be "disposable" because some filesystems cannot support them.
- Open CCC and select your backup task
- Click the "Use advanced settings" button at the bottom of the window
- Scroll down in the window and click the disclosure triangle next to "Troubleshooting"
- Check the box next to "Don't preserve extended attributes"
- Save and run the task
If a performance problem persists after that, please report the problem via CCC's Help menu.