There's been some talk about file backup and storage in this thread on shooting in RAW, but I thought I'd go ahead and start a dedicated thread for people to discuss solutions.
What's it worth?
If you're working with large files, whether they be RAW photos, PSDs, or video files, space can quickly become an issue. Obviously, gaining access to terabytes of redundant storage space isn't exactly cheap, but at the same time, my feeling is that if you have terabytes of stuff you want to back up, you've probably put a lot of blood and sweat into those files... and that blood and sweat is probably worth more than the storage space (especially for those items which are not reproduce-able). So my feeling is that it's worth making some sacrifices if necessary to make sure you're backed up, and backed up well.
Everyone has relied on a single hard drive at some point, but if it hasn't happened to you already, a single hard drive will fail (I've had four fail on me in the last two years). Typical consumer-grade hard drives fail at a rate of around 5-10% per year. So anything on one hard drive for one year has about a 1 in 10 chance of disappearing, higher when you factor in loss, theft, and hurricanes.
Having things on two drives decreases the risk of loss exponentially, because it's very unlikely that both drives will fail at the same time. So having a file on two drives typically makes it "safe," but only if you are consistently checking both drives for failures (by running a thorough test: a drive that contains corrupted sectors will likely still show up on your computer when you plug it in--but that doesn't mean that your files are safe). If you back up to an external drive, and then set it aside for months or years, only going back to it when you've lost a file, that external drive may no longer be dependable. Consequently, I would advise everyone to run thorough tests on your external drives at least once a year.
CDs and DVDs can be good options for backup, but I would suggest using them in addition to hard drive backup, rather than as a replacement (having at least two backups of your most important files--say, one on an external drive, and one on a DVD--is definitely advisable if you aren't checking the discs very regularly). The long-term reliability of optical disc storage is of yet unknown.
Another factor for consideration is "local disaster": if all your backups are stored in your house, and there's a flood or a fire, or some other unfortunate disaster, it won't matter that you had your files on three different drives: they will likely all be gone together. This is where backing up to "The Cloud" (i.e. distant computers via the internet) can be handy. There are a number of services available (Google Drive, Moby, Dropbox, etc.), though the best option for serious long-term storage, in my opinion, is a combination of Amazon's S3 + Amazon Glacier services.
The advantage of online options
Online storage options aren't cheap, but a reliable service like Amazon's is far, far more redundant and fail-safe than any local backup option you can create: Amazon replicates your data across multiple hard drives in multiple geographic regions (so if a facility burns down, you're covered), and performs regular data integrity checks on everything. The service costs $0.125 per GB per month, which is pricey, but the great thing is that you can send older files that you are no longer accessing regularly to Amazon "Glacier", which only costs $0.01 per GB per month (which is just as redundant, but less speedy to access). You can store 1 TB of data on Glacier for $120 per year. Again, not cheap, but not that much more than the price of a single 1 TB consumer-grade external hard drive: and Glacier is providing much, much more reliable storage). Still, the price barrier may be enough to keep people away who aren't "professionally" attached to their files...
Anyway, sorry that this turned into such a long post . I don't mean to be alarmist about data storage: I've just seen so many people lose precious files, that I want to do everything I can to inform people of the risks involved. One last word of warning, and then I'll quit(!): Any backup that has not been tested for retrieval (and is not being regularly tested) is not really a backup.
What do you do / think?
So... what do you guys think? What do you use and why? Do you have a foolproof backup method? Have you experienced disaster? Do you think I'm being overly cautious?