A system I use is to use a smaller ex HDD to load daily/weekly and archive each event to DVD/Blueray or whatever then when this drive is full buy one twice the size, load the smaller drive to the newer and load up to the newer drive until full, then buy another twice the size etc.
The old drives are stored away having loaded all events to DVD/Blueray and to the newer drives so there's multiple copies should any one not start again or become corrupted.
The DVD's are stored at our own business premises and HDDs at home. Each HDD is marked with the year the contents were shot.
At the moment I have nine ex HDD drives totalling about 7TB sitting on the bench each taking different events as they are shot. I have a paper log on the side detailing to which drive an event goes to and occasionally I scan the log and load to the biggest and latest drive so I can access it easily to see where an event might be.
With the occasional weddings I do I simply keep all files on backup cards until backed to 3 ex HDDs, archived on DVD then I format them.
As I shoot jpegs I really don't fill the drives up as quickly as you raw shooters do even tho I shoot about 70,000 images a year. My oldest ex HDD is now about 9yrs old and it fired up perfectly just before Christmas when I tested several (well two to be exact).