What software do you all use to backup your images?
I am using MS SyncToy for my backup but i faced some issues which i hope someone in CS can help me with.

As both my external hdd are not plugged in to the pc all the time, each time i want to backup my files/folders i only plug the hdd in. By doing so, the drive letter always change.

In MS SyncToy, the sync folders pair that I made earlier are based on the previously assigned drive letter. In the end i need to make a new pairing each time i want to sync my hdds.
Is there a solution or other software to recommend?