Just an FYI for anyone who has been experiencing slow writes to external drives when using the linux70 release candidates. I mentioned this issue a few updates ago:
Check if you have the udev-usb-sync package installed. That was the cause of the issue on my system, and removing it fixed the issue.
Many thanks to @brucew for finding the cause (and also a very good reason why Testing branch users should keep an eye on the Unstable Update topics):