The drawback to the online-storage-with-backup approach has traditionally been cost. But disk cost per byte has been plummeting at a greater-than-historical rate for the last fifteen years, and it’s now so low that, for most serious photographers, it’s not an impediment to online storage of all your images.
Why are disk prices dropping so fast? A succession of technological breakthroughs (a couple of biggies were the giant magneto-resistive effect and perpendicular recording, for you technophiles) has dramatically increased the aerial density – the amount of data that can be stored in a square inch or square centimeter. Greater aerial density means more data on the same number of platters, or even on fewer platters, which makes disks cheaper per byte stored. Greater aerial density allows smaller platters without sacrificing the amount of data stored, which makes disk drives cheaper. Greater aerial density also increases performance: when the bits are all crammed together, more of them pass the head per unit time, and data transfer rates increase. When the tracks are closer together, seek times drop. Smaller drives also dissipate less power. Increasing aerial density is a wonderful thing for computer users in general, and photographers in particular.
When an old technology is challenged by a newer one, the old technology often improves dramatically. This has been the situation with disk storage. Twenty years ago, most technologists believed that by now, disk storage technology would have been substantially replaced by now with flash memory. That hasn’t happened, not because flash memory has failed to advance as predicted, but because disk storage has evolved faster than most people thought it would. This has been a good thing for photographers, especially in the last ten years when the size of digitally captured images has been increasing quickly (but not as quickly as disk drive capacity). Today, leaving out scanning backs, the upper end of the size of digitally captured images is around 80 megapixels for medium format cameras and about 35 megapixels for 35mm sized cameras. Over the next five years, these numbers might double, (or quadruple if camera manufacturers decide to oversample and eliminate the antialiasing filters. If disk technology continues to advance in the next five years at anywhere near the rate of the last 10 years, the economics of storing all your images on disk will become more attractive as time goes by. Eventually, rotating magnetic memory will be replaced by some other kind of nonvolatile online mass storage, and what I have to say about storing your images on disk will probably apply equally well to that storage medium.
Let’s test my contention that disk storage has become sufficiently affordable by working out some examples with today’s pricing. If you have 10,000 raw images from a 24 megapixel camera, at 16 bits per pixel you have half a terabyte of data. You can buy a 3 terabyte external disk for $140 to $200, so it will cost you about $80 to store all those images. Let’s say you are a prolific shooter and a terrible editor, with 100,000 raw images. Basic storage for those images is less than $1000. Maybe you do a lot of editing and love layers, so you’ve got to store big Photoshop or TIFF files. If your files are 500 megabytes apiece, you can store 6000 images on that under-two-hundred-buck disk.
It’s not all good news. That’s just the beginning of what it will cost you to store your data dependably. Disk reliability has made great strides over the 50-year history of the device, with calculated mean time between failures now coming in at over 100 years, and field failure rates of possibly a half to a quarter of that. All the same, a sensible attitude towards a disk is to view it as a failure just waiting to happen, and to arrange things so that, when disks die, you can easily replace them and restore your data. A disk failure may be an occasion for a mildly elevated pulse, but it should not cause panic.