Backing up digi supplies

[knittingbec]

I sat down to scrapbook this morning & my external hard drive was not being recognized by my laptop. :/ I plugged it in a different port & my whole screen went black. Yikes!
Luckily, it opened on my husband's computer & I finished backing up a few months of photos that I hadn't copied onto our other EHD. (I also upload my photos to smugmug for backup)

My question for you is this:
When you back up your digi supplies, do you drag & drop all and then tell it to skip the duplicates, or do you just copy over the stuff you've added since your last back-up? If you do it the second way, how do you know what's new and what's already backed-up?
I'm doing it the first way right now, but it's taking ages.

Or maybe there's a different way that's so much better and I'm just not thinking of it! Tell me what your process is...