Suppose that you're looking for a robust and scalable RAID array solution to store your important enterprise data. You need to consider the fault tolerance of the RAID array, the RAID array manageability tools, support for dynamic growth of the RAID array, support for additional disk drives, and the I/O technology in place.
Fault Tolerance of the RAID Array
Regardless of how well you tune and size your RAID array, it can still fail to a point at which you can't access your data. The importance of your data directly affects the level of fault tolerance that you apply to your RAID array solution. Improved fault tolerance is synonymous with higher cost. If you use a RAID level other than RAID 0, you've already decided that your data has some level of importance because you're providing disk-level redundancy in the form of RAID. Beyond this precaution, consider these desirable fault-tolerant features to further bolster your overall RAID array solution: redundant hot-swappable power supplies, redundant hot-swappable fans, and hot-swappable hard disks. These items are becoming more common, and you should consider them mandatory.
Some external RAID arrays, such as those from Data General and Symbios, provide embedded RAID array controllers. These units internally support multiple SCSI channels to each hard disk so that if one disk array adapter channel fails, you can still access the disks in the array. For the ultimate in RAID array reliability, you can add multiple RAID array adapters in your server, where each provides a separate channel to your RAID array. Again, if one RAID array adapter fails, the server—and subsequently your customers—can still access the information on the array. You can also leverage these extra channels for improved performance of larger RAID arrays. Whenever possible, try to remove single points of failure.