We are, as of today, the proud owners of a new external hard drive with two terabytes of storage capacity--the whole room feels bigger, somehow.
Two terabytes of data (which I still cannot say without thinking of pterodactyls, which might suit an "historical" room better--but I think digital storage will be more useful to us than two flying reptiles): in 2006, R. David Lankes compared this amount of data storage capacity to an academic research library, but clearly he was thinking text rather than images. Our 250 Mb external drive, which we received a short time ago, has 70 Mb of free space remaining--and we've barely begun to utilize our new large format scanner.
Our digitization policy calls for scans to be a minimum of 600 dpi, in uncompressed tiff format. We have found that this size is generally adequate for any derivative products we or patrons might need to use (from prints to web images), although we have scanned a few things at higher resolutions when trying to get the best image possible. We scan pretty much everything in 24 bit color, too, even the black-and-white photographs, because the color captures the nature of the original so much more fully than a grayscale scan. Sepia tones, coffee stains, editorial marks--our scans are intended to represent the original physical item to the maximum extent possible; derivative files can be cleaned, cropped, and generally "prettified" depending on the intended use.
So, while our 2T drive may not be able to hold our entire Historical Image Collection, for example, it will go a long way towards giving us some breathing room. What's our backup plan, the savvy tech user asks? Our backup is the OHSU Digital Resources Library, and its backup plan is maintained and executed by the university IT folks.