Hi Don,
There are two issues here that I think best to examine independently:
- bettering your workflow to end up with all Images' Originals on your external drive
- backing up your Library and your Originals.
I use a separate disc to keep all the masters on so that I do not fill up the iMac disc. Is there a way to have this done automatically and if so can some tell me how ?
Yes. When you import any file, tell Aperture to store that file (on import, it becomes an Image's Original) on your external drive. On the "Aperture Library" section of the Import dialog, select your external drive from the drop-down "Store Files", and select the radio button "Move Files". You will end up with newly-imported Images in your Aperture Library, each of which will have an Original on your external drive.
That may resolve your "duplicate masters" problem. ("Master" is the older term for "Original". They are synonyms.)
When you back up your system, be sure to include your external drive. If you use Time Machine, it should be included automatically (all connected drives are by default), but you should check your Time Machine settings to make sure, and then check your back-up to be even surer š .
Your follow-up question might be: "How can I tell which of these files is an Original of one of my Images in my Library? If so, let us know.
HTH,
--Kirby.