Properly "killing" an older W10 installation

Kupuna · 22 Jun 2016

I just put in a new SSD and have been in the process of transferring and reinstalling files and apps from my older Win 10 main hard drive to the new SSD. Through the UEFI Bios, I can still boot into either old or new disk but I notice that there may be increasing glitches at the hardware level as I move from drive to drive.
I would like to deactivate the Win 10 aspect of the old drive. Then I could open it from the new drive and copy data to its new home.
Am I correct in guessing that even when the old main drive is not booted, it's presence might still cause problems because of its hardware and driver interactions? One thought I have is to fully back up the old drive to my spacious backup drive, then pick up the pieces I might need later from there. I use Macrium Reflect for backup, so I can break out individual files, although it is more difficult than copying them from their present location.
I feel like I am making this too complex, but I don't want to rush and wipe out data I might need.

CountMike · 22 Jun 2016

Best way would be to back up all files you need from that old drive somewhere else and than delete all partitions from it because you will not need them for data drive and they are just taking space. You can re-partition it at will and return files to it from the backup.