I suppose I should apologize for the fact that I tend to hound my readers on the
subject of backups. Hmm. Nah. 
Well, I do apologize to those of you who
already know to do backups and actually do them, but unfortunately, you by far represent
the minority of PC users. Lack of proper backup procedures is risky at any time, but with
some types of RAID, especially RAID 0, it becomes riskier than ever.
Most RAID levels use striping, which causes most of the
files on the system to be "chopped up" into small pieces and distributed to
various drives in the array. This improves performance but poses a real risk to the
integrity of your data. If a drive goes on a striped array, "some part" of
almost every file in the system is gone, and there's really no way to figure out what is
gone. A fault-tolerant array that includes parity protection
eliminates much of this risk by allowing a single drive to fail, but a RAID 0 array does not. Since arrays have much lower
hardware reliability than individual drives, this means the odds
of a catastrophic, near-unrecoverable failure on a RAID 0 array are higher than most
people realize. (Data recovery companies can
sometimes perform miracles; frankly, if your data is important enough to warrant spending
what a recovery service would charge to reconstruct a RAID 0 array, it's important enough
that it shouldn't be on a RAID 0 array. An ounce of prevention and all that...)
If you are using mirroring, either by itself or in
combination with another technique, your odds of losing your data due specifically to
hardware failure are greatly reduced, but they are far from zero. Regardless, there are a
host of other problems that could wipe out your data:
- Unexpected Hard Disk Failures: It's not unheard of for two mirrored
drives to fail simultaneously, especially if they are the exact same make and model and
came from the same lot. Sometimes manufacturers have a "bad run" and the failure
rate of a particular batch of drives is very high.
- Failures of Support Hardware: The other
hardware that runs the entire array can fail. Power supplies fail, or a motherboard
develops a problem due to overheating, or memory goes bad. These can cause either outright
failure of the array, or even worse, gradual corruption in some circumstances.
- Physical Damage: Due to natural disasters, carelessness or sabotage,
your hardware could be physically damaged. This will affect all or most of the drives in
the array.
- Software Problems: Software has bugs. This includes all operating
systems, although some are much better than others. Bugs can lead to data loss.
- Viruses: A virus can wipe out individual files or entire disk volumes
at the system level; no form of RAID will help you.
- Human Error: This is one of the leading causes of data loss; again,
RAID will not protect you against an accidental file deletion, formatting the wrong
partition, etc.
That's not a comprehensive list, but it's good enough to make my point: even a robust
RAID implementation does not replace proper backup
procedures. The more you can afford to put together a good RAID system, the more
important your data is, and the more you should spend on a good backup system.
Next: Data Recovery
