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(This is one of many pages of tips on Organizing Your Images.) In order to make reasonable decisions about how to backup our images, we need to examine some of the media available and their cost, speed, reliability, etc.
The transfer rates and times were based on tests I did in June, 2008 using a fairly new, fast machine. The average times to transfer 4GB (in Minutes:Seconds) are shown to give you a feel for time it takes to copy (backup) what I recommend as the reasonable maximum folder size. Your times may differ, but I'm sure the relative times and the conclusions will be about the same. Details: DVDs: In the past I've always backed up my images on CD, but the files produced by newer cameras are so large that only DVDs currently make any sense. Because CDs and DVDs have a fairly high failure rate, I've always recommended making a mininum of at least THREE copies (see "CD failures" below). The times given are the actual write time ... in fact the total time is MUCH longer when you consider setting up the archive job, changing and labeling DVDs, etc. Some people claim that writing DVDs at lower speeds, makes them more readable; I think it may improve your chance of being able to read them on other machines, but I'm not sure it increases how long they last. (Of course since you'll probably have a different machine in the future it may help.) The 90 sec/GB time I show was writing at 16x, but I don't think my machine actually writes that fast. I'll typically use premium 8x DVDs (which cost less than 16x DVDs). Writing to a 16x DVD at 8x I saw transfer rates of 128 sec/GB; at 4x it was 216 sec/GB.
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External Hard Drive via USB 2: Failure rate of individual sectors is VERY low, in fact it's so infrequent you'll almost never loose individual files. But, of course when the drive fails you loose everything on it 
. Biggest issue with external drives is cooling; letting them go to sleep (spin-down) automatically or turning them off when not in use will lower the failure rate. (Keeping them turned off most of the time will also help protect against computer failures or viruses that might wipe-out the drive.)
Price per GB (20 cents) is based on the July, 2008 internet sale price of a WD 500GB drive ($100 delivered, no tax). I own several of these WD drives and have had good luck with them.
Flash Drive: Makes no sense except maybe for temporary backup. I included it in this list only because I was interested in comparing the transfer rates. They were MUCH lower than I expected. I think this is because the flash drive I tested was VERY cheap when I bought it a few months ago and probably doesn't match the specs of a better flash drive. (Be careful how you connect any flash drive or media card to your computer, you'll often be using a USB hub and many will slow down the transfer. Do some tests of your own. As I remember these times were read times, write times are going to be longer. Rule-of-thumb, if it's taking more than about a second an image to transfer your images explore alternative connections.)
Price per GB ($3) is based on a February, 2008 purchase of an 8GB drive for $24. Each week you'll find a better deal somewhere. I highly recommend flash drives for file transfer (when machine's aren't networked) and you might use them for temporary backup, or as part of a daily backup strategy.
Internal SATA Hard Drive: Failure rate is very low. A good workstation tower usually has better cooling than an a drive mounted in an external enclosure. In older machines hard drives were connected using IDE (wide, flat cables) which were slower. The newer SATA connections are faster. I know most new machines are built with SATA DVD drives as well (probably a bit faster), but since I recommend extra internal hard drives, I build machines with IDE DVD drives which leaves the SATA connections for internal hard drives.
Price per GB (16 cents) is based on the July, 2008 internet sale price of a 500GB drive ($80 delivered, no tax). Currently I recommend 750GB drives because their price per GB is probably less than a cent per GB more and they allow you 50% storage in the same machine (you are limited by the number of drives that fit in your case and that your motherboard supports). Normally I avoid buying the current biggest drive (1TB when last I bought drives) because they ALWAYS cost 40-50% more per GB than the next smaller size. (The cost difference may go down just before the next bigger size is available, but when it does the new, bigger size is almost always been 50% more per GB more.)
Network Hard Drives: When you get a new computer, keep your old one. Attach it to a local network (which isn't hard at all). Either let your spouse use it, or treat it as an external backup drive that you can also use as a backup computer in the case your new one fails. For information on sharing and mounting see Network Drives.
Price is the same as other internal hard drives, they're just on a different machine. Fact is that since you probably have the machine and the drive, the cost is zero.
Bottom Line: Given the current low cost of hard drives it no longer makes any sense to use CDs or DVDs as your primary backup, but I still highly recommend keeping one or two copies of your original images off-site on DVD. Make sure you off-site copy is far enough away that it won't be destroyed in the same fire, flood, theft, hurricane, or other disaster that causes you to loose your primary copies.
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