@Proton2:Not Win8 only, but personally, I just drag out tools like Acronis to do disk-disk cloning of running systems. I've also got a few nifty USB-SATA adapters for those situations where there is only a single SATA connector (like a notebook). I recently converted a running laptop from HDD to SSD and had no issues with this approach, and it leaves the original HDD as-is, just in case.

Of course, your target drive needs to be large enough to clone the source drive's data, but most commercial cloning software is at least smart enough to clone the data of a larger disk to a smaller target (like an SSD) provided the data doesn't exceed the target capacity.