Using RAID SCSI controllers on servers is the easiest way to gain disk subsystem performance and reliability. Within the past year, the availability of RAID controllers for workstation-class systems has increased. Vendors such as HP and IBM offer products with built-in SCSI controllers that support a special add-in card that provides hardware support.
RAID levels 0 (striping), 1 (mirroring), and 5 (striping with parity) are the most popular options available. RAID 1 has the highest level of reliability, RAID 0 has the fastest performance, and RAID 5 has an excellent compromise between reliability and performance. Some vendors offer controllers that support the RAID 0+1 configuration. If you combine RAID 0 and RAID 1, you get the best of both worlds.
Multiple channels (independent SCSI buses) are also helpful because they limit the number of PCI slots that the disk controllers occupy. You can easily find controller cards with three channels.
You can find support for all SCSI versions (e.g., I, II, III, Wide, Ultra, Fast) in most higher-end controllers, and technology advances let you mix different speed devices on the same SCSI bus without affecting the speed of the higher performance devices. Single-channel cards can now provide much-improved performance when supporting mixed-speed peripheral devices such as hard disks and CD-ROMs.
Although you can spend thousands of dollars for the high-end SCSI RAID controllers, the starting price for cards that offer more than basic features has dropped to a few hundred dollars. This price reduction makes RAID a must-have option for servers you use for serious business needs.
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Corrections to this Article:
- Buyer's Guide: "Raid Controller Cards" in the print magazine contained incorrect information about RAID levels 0 and 1. RAID 0 is striping; RAID 1 is mirroring. Of the three most popular RAID options (RAID levels 0, 1, and 5), RAID 0 has the fastest performance. RAID 1 has the highest level of reliability, and RAID 5 offers an excellent compromise between performance and reliability. We apologize for any inconvenience these errors might have caused.
