Everything.
Save it on your computer drive, back it up to your Time Machine hard drive, then back this up to your Drobo, then burn CD's of the files, then print them out on an Epson printer, then rephotograph the prints with a 35mm copy camera and archivally process the film. Then store it in acid-free sleeves in a fireproof contaner.
Then take the discs and the film and the prints and any spare pixels that have fallen out of the back of the machine and put them in a safe deposit box down at the Bank of New South Wales.
You may want to ask the bank to sandbag the St. George's Terrace entrance and post guards armed with Stirling SMG's there - better safe than sorry.
After you have done this, go back and look at the images you started with. Are they really all that good? Is your student portfolio of 365 daily images of a banana on a plate really the stuff of your dreams? Have you advanced? Would it be a good idea to keep one picture of the banana and clean the rest out of the drive?
Just this thought occurred to me some time ago when I noted that the content level indicator on the Drobo drive I use got past half-full. Now the Drobo is a wonderful device for keeping things safe, as long as you keep it safe. I can re-disc it to far more capacity than it bears now...I'll do that eventually, but decided to look into the thing at present to discover what was in there.
Well, I didn't find the missing sock but I did find damn near everything else that I had dumped into it. Including jobs that had a set of RAW files, jpeg finder files, working psd files, and finished jpeg output files. Plus a few tiff's and something that looks suspiciously like a tram ticket. It was like an overgrown garden of pixels.
I set aside my ruth and weeded relentlessly - gaining back valuable disc space and concentrating each division into work that I am happy with. I did allow some wiggle room with RAW files that I may re-work...but even there I have been realistic with what was actually worth re-working. Let's face it folks, we usually get better as we go along, and it is retrograde to go back and try to make silk purses out of our sow's ears. They are never good and it annoys the sows.
Spring cleaning is not just for the carpet - try it and see.
