Comparing SATA RAID and SCSI RAID

I've noticed that many new motherboards come with Serial ATA (SATA) RAID options. My company is in the process of replacing some old SCSI RAID—based servers, and we're considering purchasing some SATA RAID—enabled systems. What are the advantages and disadvantages of SATA RAID compared with SCSI RAID?

SCSI RAID and SATA RAID aren't exactly in direct competition; both satisfy different needs. SCSI (or the higher-bandwidth Fibre Channel) provides high-performance, multitasking RAID systems, whereas SATA RAID provides inexpensive fault tolerance.

SCSI and Fibre Channel are the tried-and-true choices for high-end RAID systems that support financial or other crucial data. Furthermore, the cables that SCSI systems use let you conveniently attach external storage to a server. And, primarily because of the SCSI chipset's bus-mastering capabilities (i.e., because the chipset does the bulk of the work involved in sending data to the server processor), the commands for SCSI transfer let multiple users multitask with ease. ATA was developed as an inexpensive, nonmultitasking alternative for desktops. Current ATA cable length is limited to 18", making inconceivable the thought of ATA satisfying any aspect of serious server RAID. Even though SATA does away with this 18" limitation, SATA RAID just isn't a realistic alternative to the more expensive SCSI systems when you must meet a need for high performance.

When cost is the main concern, however, or when availability of data is more important than rate of transfer, SATA RAID is an excellent choice. SCSI and Fibre Channel are available in 10,000rpm and 15,000rpm models; large SATA drives are currently available only in 7200rpm models. A 37GB 10,000rpm SCSI drive costs $175, a 37GB 15,000rpm SCSI drive costs $350, and a 74GB 15,000rpm drive costs $700. In comparison, a 37GB SATA drive costs $125, and a 160GB SATA drive costs about $150. You can place five 160GB 7200rpm SATA drives in a RAID 5 configuration for the price of one 74GB 15,000rpm SCSI drive. The SATA array won't approach the performance of the SCSI drive, but for the same price, the SATA array gives you the fault tolerance of RAID 5. As SATA RAID matures, its usefulness in these types of situations is sure to increase.

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