A good backup strategy has to be reliable, robust & have a redundancy plan. Many professional photographers have incorporated image management applications into their workflows, applications like Aperture by Apple and Adobe Lightroom. These applications are great tools and should be used by all photographers who are serious about organizing image libraries on a large scale. At all cost avoid being caught up in an information silo. An information silo is a management system that is incompatible of operating with other related management systems. This means keeping the image files in a format readable by alternative applications and avoiding having them tied up in application managed libraries or folders. If you do decide to use an application managed library you then need to make sure you can get out what you put in. If you import RAW files, you need to be able to pull out the original RAW files for that worst case scenario. A good practice would be to import the master files into a user created folder and use this as a referenced library that would easily be accessible by alternative applications.
Backing up the master files is the first stage and it's important to have at least three copies. The more copies the better but it's also important to be smart about your backups. There is no advantage to having 100 copies of the master files in the same room in the event of a fire! That may sound extreme but planning for the worst case scenario should keep your data safe.
Keeping a local hard copy of the master files is the first backup action. A local hard copy would be the most accessible and the first copy you would turn to if needed. Firstly, backup the master files to a CD or DVD and store these away in a safe place. The easiest and most flexible storage format to use would be an external hard drive using a USB or FireWire connection. Using a RAID 1 drive would provide extra security against data loss. RAID 1 drives contain two physical disks which mirror each other so if one were to fail the data would be accessible from the other.
The second stage of a backup plan should be to create a second hard copy using a RAID 1 drive but to store this drive at a different premise and not under the same roof. This adds extra security and would protect against fire and theft. The second aspect to off-site backup is to use a cloud based storage system. There are plenty of options for uploading data for storage, I would not use this as a main storage solution but it adds another layer of protection and the cost is quite small. Some of the more popular cloud storage providers are Carbonite, CrashPlan, Mozy and JungleDisk.
Just by following all these steps the copies you would have are as follows:
A main copy on the computer, a local copy on CD / DVD or both, a local copy on a RAID 1 drive, off-site copies on a RAID 1 drive and finally the off-site copy stored on a cloud based service. What is very important is to make sure the data is readable after backing it all up. Once a copy has been made, access the data and make sure it can be read. The options and steps stated are quite straightforward and should offer plenty of protection against data loss.