If you have your Web site or a network server in-house, or you can't afford a moment of downtime due to hardware failure, you may need to build a custom solution that involves redundant hard drives or a backup server. You may want to consider RAID, redundant servers, and/or removable hard drives. RAID (redundant array of independent disks) is a configuration of one or more hard disk drives that work together to increase performance and/or fault tolerance. A set of RAID drives comes with a special hard drive controller with RAID functionality built into it. RAID improves performance by striping data (interleaving it) across multiple drives, so that more than one disk drive is reading and writing data at the same time, which allows several disk drives do the task of one drive and improves the speed. RAID provides fault protection (protects against data loss due to hard drive failure) by using one of two techniques: mirroring or parity.
RAID: RAID is available for either the Mac or PC. A RAID controller adds $300 to $2,000 onto the cost of a server. The difference in price depends the levels of RAID supported and the number of channels. The higher the number of channels, the faster the controller and hard drives can communicate. You'll also need to factor in the cost of the extra drives needed to support RAID.
Windows NT 4.0 ships with a feature that allows software control of RAID, eliminating the need for a separate hardware controller. However, you'll need to be aware of the limitations of software RAID. Software RAID uses the computer's CPU, rather than a separate CPU on the controller, slowing down system performance. It can also be difficult to configure.
If you're interested in RAID, your best bet is to look for a server that comes with a RAID controller that is preconfigured for you. This will save you the extra expense and time of adding RAID to an existing system.