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#21
As I already suggested is to install a HDD or SSD internally and attach the power cable only when you're going to use it.
You don't need to clone the whole disk very often. You can clone the whole disk once every three months or when you install a new program or do a big upgrade.
For the data backup you should do at least once a week. Instead of cloning the whole disk you use a backup program that compares what you have on the main drive with the backup drive and only updates what has change on the main drive. This only takes 5 minutes.