If you frequently use virtual machine container files (e.g. with Parallels, VMWare, VirtualBox, etc.), you may find that CCC's SafetyNet folder tends to get very large, very quickly, or that snapshots on the destination consume space very quickly. Every time you open your virtual machine, the monolithic virtual machine container file is modified, and CCC will require that it gets backed up during the next backup task. If the SafetyNet is on, CCC will move the older version of the VM container file into the SafetyNet folder (or it will be retained by a snapshot on the destination).