Thank you for your suggestions.

I do have an UPS - impossible to work without here.
At the moment I have one external drive that gets plugged in only when I need to do a backup, but I would like at least one more. So yes, RAID1 seems to be a good solution.
Well, the advantage of having the two drives mirror-image connected seems to be only saving the data in case of disk failure. The rest work as if you would have a single drive.

What characteristics must the drives have to be set in RAID? Identical model, size...