Backing up your data is one of the most important steps in in the modern photographic process. Digital actually allows for the making of multiple copies. I will focus on using a mac for specifics, but keep in mind that the basic concept applies across all platforms.

PUT YOUR DATA ON MORE THAN ONE DEVICE. IN MORE THAN ONE PLACE.

It is actually that simple. However you want to do it is fine. There are programs that copy your entire harddrive to an external drive automatically, there are programs that do it so that you can pull that backup out and stick it in your main computer if the main fails. I am going to outline my setup, as always, your milage may vary…

The main problem with ALL backups is that they WILL fail. Always, every single one, every single time. This is true of floppy discs, CDs, DVDs, Blu-Rays, hard disks, and flash devices.

Main Computer
My main machine is a MacBook Pro (MBP). Sure it is highly virus/hack/spyware/malware resistant, but it is not spilling a drink/dropping or getting hit by a bus proof, and it is most certainly not theft-proof. My MBP is running the latest and greatest snow leopard (10.6) and I am fortunate enough to have a plethora of hard drives at my disposal. The best way to back up your mac is through the built in Time Machine utility. It is super easy to setup and will backup every hour automatically, so long as the backup drive is available. It also makes rolling back to older files very easy. I recommend a larger hard drive than the one being backed up as it allows room for history as well as other files and is more future proof.

Additional Files
What if you have files that do not reside on the drive in your computer? So you have made the jump and have begun using an external hard drive. As your main computer gets bogged down with stuff you begin to move files and folders over to that other drive, which is commendable as you are freeing up space, which keeps your machine tidy and therefore faster and less buggy. Also, diversifying your data across more than one device is a way to decrease the odds that you will lose everything in a mechanical/software failure. The problem is multifaceted.

Not only will the drive fail at some point, most likely the most inconvenient time. It is also by its very nature relatively portable. This portability increases the likelihood of theft and loss incredibly. It also increases the likelihood of physical damage from drops, bumps, and abuse. The best thing to do is to be highly organized and make sure that the data on the drive is in more than one place.

Application of New Knowledge
There are endless combinations of backup schemes, however, I will outline a few simple options below.

1. A Time Machine drive setup to mirror what is on your laptop and you have no other external drives. This is a good starting place and can help you to acclimate to the idea of backing up. I still highly recommend that you burn discs of important files and store them with a friend/family member to protect against fire/flood/theft.
2. A Time Machine drive setup to mirror what is on your laptop and external drives that hold other information. The simplest way to execute this is to have 2 identical drives that are labeled something like Drive1 and Drive2. Make sure that they have the SAME folder structure and drag and drop files to both drives every time you move something to 1 and 2.

Here is a slightly more complex but more automated option.

1. A Time Machine drive setup to mirror what is on your laptop and external drives that hold other information. The difference here is that you can actually use software to mirror one drive to another, sort of like Time Machine does. This allows for a more hands off approach and does not require you to carry 2 drives around all the time. I highly recommend carbon copy cloner by bombich software. It is relatively straightforward and has excellent help files.

This is the most expensive but easiest option.

1. Purchase a Time Capsule device, follow the setup instructions and your machine will automatically backup whenever you join your wireless network. I still HIGHLY recommend the burning of discs of important files as well and storing them off-site.

What Should I Buy
Almost all major hard drive brands are good these days. I highly recommend Seagate and Western Digital. I also like LaCie drives, however, their warranty tends to be shorter. If you are on a tight budget and possess a basic ability to operate a small screw driver, then it is very easy to build your own drive from an enclosure and bare drive. A quick search online will reveal plenty of information on what you need. This generally yields a higher quality/lower cost and more useful drive later on down the road. I would suggest comparing prices between newegg.com and amazon.com. I also like to throw in that I highly discourage buying a used hard drive, as you have no idea what it has been through.