Not so long ago, it was a miracle that computers came with a 20-gigabyte hard drive. When 40 gig drives hit the market, the world was astounded. Now, a 1-terabyte drive barely registers on the "wow" meter. For most folks, this kind of storage is far more than they'll ever need. For those who edit video, the volume of storage is important, but so is the ability to rely on the drives to contain and play out the images. However, should that single drive fail, the project is either destroyed or it's back to square one and starting over.

The solution to the catastrophic failure problem came in 1987 when some college students at the University of California, Berkeley invented a system called Redundant Array of Independent Disks or "RAID" for short. The solution depends on a series of two, three, four, five or more hard disc drives connected together so that all of the drives contain the necessary data to complete a given project. The RAID system is designed so if one of the drives should fail, then the other drive(s) contain redundant data that rebuild the failed drive. Additionally, the computer will recognize the array as a single, huge drive.

A RAID system is not just for storage, but is an ideal way to keep and retrieve video too. A byproduct of the array is an increased throughput as many drives can be accessed at once and this means easier, faster editing as video images are retrieved much more quickly. But, like most technology, it's best to have a little information before buying. Beware! Simply having a RAID array will still not protect you from viruses, worms or other nasties that may infect your drive. An array is no substitute for a good anti-virus and firewall.

RAID Geek Speak

In its simplest form, a two drive RAID array (Called "RAID 1"), one drive is a complete copy (called a "mirror") of the other drive. So if Drive A fails, then Drive B will contain a perfect copy of the data to rebuild drive A once the failed drive is replaced.

The other most common form of a RAID is called "RAID 5" (for an explanation of different forms of RAID arrays, see sidebar). In a RAID 5 array, all data is separated and distributed in small bits across all drives in a process called "striping". All of the stripes have perfect copies on two or more additional drives in the array in addition to the original drive. So, if one drive should fail, its blank replacement can be rebuilt from the redundant bits from the other arrays. Should one or more drive fail at the same time, it's still possible- through software, redundant striping and error correction- to rebuild and regain lost data from the other working drives.

Most of these systems use something called "parity" where an area of storage is set aside - not for storing data - but for the error correction and replacement of missing data. When a drive fails, the parity information is used to rebuild the replacement drive.

RAID is more than a stack of hard drives wired together. Yes, it's a system of storage, but also a method of rebuilding failed drives, a way to increase access to data and a simple way to ensure the video you're editing stays safe and pristine.

So, Which One for Me?

Your pattern of use helps determine your needs as far as choosing a RAID system goes. If you are an enormous user and consumer of video, music, photos and data- if you store your movies on hard drives, than the size of each drive is an important factor. If editing is more of what you want to do, than throughput will be more important as it's imperative that the computer be able to move data quickly from the drive to the computer and back.

The size of your array depends largely on your budget. In the case of video production, larger drives are better because video, especially HD video files, which consume enormous amounts of data and space on every drive. A raid 3 array with three 500GB drives will have 1TB of storage (one of the 500G drives is needed for "parity"). Start saving your money now. Luckily, drive prices are getting cheaper daily.

RAID systems can be purchased as an external box separate from the computer itself. Inside these boxes are the drives, cooling fans, power supply, all the wiring and the RAID controller. The RAID controller does just that- it manages all of the drives and presents them to the computer as a single storage item.

Also look for the ability to "Hot swap". This means that the drives can be replaced while the unit is operating without causing any damage or delay to the array system. Some less expensive units may require complete shutdown before removal of the drive and this can cause long-term delays and lower productivity.

Easy setup is important too- Check user reviews to see which manufacturer provides easy to use software, the necessary cables and good customer support to get your array up and running. If you're something of a computer savvy geek (that's a compliment, by the way) you might not need the level of help that someone with less skill and expertise would need to start their own array. Fortunately, most name brand manufacturers have figured out user friendly approaches to a problem-free setup.