I have a 1 terabyte RAID5 TeraStation hard drive array, made by Buffalo Technology. It isn't a speed demon, but it gets the job done. My primary working drive is a 500GB 7200 rpm drive in my desktop workstation. All of my more recent raw images and layered .psd files are accessed on this drive. Every night these files are backed up to my RAID5 server through the use of Retrospect backup software.
Once a month I back up my RAID5 server to offline USB hard drives. These drives are in varying sizes from 160GB to 300GB in size. It takes me some manual moving around of files, because no single drive can hold enough folders that need to stay together as one cohesive group. In other words, one drive might have baby photos mixed up with African safari photos. Not optimal.
So I am revamping my entire backup strategy in the coming weeks. I plan on turning my Dell desktop workstation into a RAID server of some kind. I am also thinking of buying a 1.6TB ReadyNAS RAID5 server for an additional backup server, as my digital photo library grows by about 200GB per year (yes, you have that correct!). The ReadyNAS is apparently much faster in retrieving and saving files compared to my TeraStation solution. So my backup plan will work like this:
After a shoot, files will be transferred from my MacBook to my Dell desktop with two 500GB drives inside. On a nightly basis, these files will then be backed up to the ReadyNAS 1.6TB (1.2TB usable) server. Once a month I will backup the ReadyNAS data to the TeraStation 1TB server (750GB usable) and any additional external hard drive(s). I will then take these devices off site to a family member's house. Since my library is growing so quickly, I anticipate that the Buffalo server will only contain older shooting sessions from years past, and it is not likely that they will change at all. So my monthly off location backup will most likely only be a USB drive or two.
I am just thinking off of the top of my head, and these ideas might change while I am sketching everything out on my way to Alaska on Saturday. I will have over 7 hours to think about it!