I'm getting ready to buy new harddrives. I'm also going to be permanantly archiving a large number of photos.
How do I ensure that all my DNGs have their edits "hardcoded" to the files and are not soley dependant on the LR catalog DB.
Lightroom is a non-destructive editor, which means it NEVER changes the images in the source files. The edits that are applied to make what you see or export ALWAYS come from the catalog and ONLY the catalog.
That said, you can bake those edits in by exporting, or save them as (xmp) metadata by pressing Ctrl/Cmd-S, and you should backup your catalog religiously.
It is possible to add your exports back to catalog then delete originals (thus permanently "hardcoding" your edits into new versions of your source files), but a highly recommend that you do NOT do that, unless your needs are truly special, in which case I can't help but question if a non-destructive editor is the best fit.