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In the enterprise storage array market, SCSI has traditionally been the only game in town. IT managers rarely think twice about rubber-stamping orders for disk arrays using high-end SCSI hardware, especially for use in data centers and other mission-critical environments.
Today, however, SCSI may be losing its iron grip on the enterprise RAID market. A growing number of storage vendors have introduced ATA-based RAID products that offer solid - and rapidly improving - performance and reliability, combined with management tools suitable for enterprise applications. Many of these products are designed primarily for disk-to-disk backup applications.
Analysts, vendors and end users generally agree that SCSI-based RAID is still the best choice for volatile, high-intensity applications such as databases.
Yet many analysts also predict that ATA technology, as well as new products based on the next-generation Serial ATA standard will eventually challenge SCSI even in the high-end enterprise RAID market. "In the past," says Tim Klein, CEO of ExaDrive Networks, Sunnyvale, CA, "we fought the perception that ATA was all junk and that a company's data was too important to be put onto ATA. That has settled down - people understand that ATA is real, it's reliable and you can count on it."
How low can it go?
The price gap between SCSI and ATA drives is wide. As the cost of 1TB of raw ATA-based disk storage falls in some cases to less than $1.25 per GB, the gap has widened into a canyon. Many retailers, for example, now offer brand-name 80GB 7,200 rpm ATA/100 drives for less than $100; by comparison, a typical 73.4GB 10,000 rpm Ultra160 SCSI drive can cost over $350, or more than four times as much per GB.
At the same time, 7,200 rpm ATA drives with capacities up to 200GB are now widely available for less than $2 per GB. Only a handful of Ultra160 SCSI drives exceed 80GB, by comparison, and those that do carry a whopping price tag - typically $6 to $7 per GB. "The ability to get a half terabyte of storage with just four ATA drives is incredible if you think about it," says David Vaughn, a product manager in IBM's storage networking division. "We now have the ability to provide an enormous amount of storage at a very low cost."
In addition, performance and reliability differences between SCSI and ATA have narrowed, and according to industry analysts, these differences become even less significant in array-based configurations. "With more than five drives in an array, you saturate the bus on just about any system out there, and you can't take advantage of the faster data transfer provided by higher [SCSI drive] spin rates," says Bob Ripley, vice president of marketing for Consensys. "If a SCSI drive spins out data three times faster per drive on a large array, all you're doing is generating heat."
Some industry experts also challenge the assumption that ATA disks aren't reliable enough for enterprise use. "I haven't heard any derogatory statements made about ATA reliability, and in many cases I hear just the opposite - ATA drives can be more reliable than some SCSI and Fibre Channel [FC] drives," says Peter Gerr, research analyst for the Enterprise Storage Group, Milford, MA. And with MTBF rates on ATA drives of 30 years or more, disk failures in RAID systems are a real problem only for the most critical enterprise applications.
Gerr also stated that so far, SCSI vendors haven't moved much to cut prices on their products, although that could change. "There's the potential for downward price pressure on SCSI and Fibre Channel products, but it's still too early to tell," he says.
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