To avoid possible data loss issues after restoring a mobile account’s Home from a backup, do not restore (~/.Filesync), (~/Library/Mirrors), or (~/Library/FileSync).

To avoid this issue, always exclude the ~/.Filesync, (~/Library/Mirrors) and (~/Library/FileSync) folders when creating a mobile account.

Source: Apple.com

dd bs=512 if=/dev/rXX# of=/some_dir/foo.dmg conv=noerror,sync
bs : blocksize
if : unix path to the actual disk device
of : destination directory
noerror: skip errors
sync: fill nulls for errors
Source: MacOsxHints.com