Where ATA arrays can save you money


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New vendors
A growing number of vendors now offer ATA-based RAID products. Many of these firms focus on the small business and low-end server markets with RAID products supporting a small number of direct-attached ATA drives. Others have focused on "RAID on a chip" ASIC solutions designed to move disk array support onto the system motherboard.

But a handful of companies - including 3ware, Consensys, and ExaDrive - have set their sights on the enterprise RAID market. These firms have developed ATA-based direct- or network-attached RAID products designed to match or even exceed the performance of SCSI- or Fibre-based arrays. Consensys' Raidzone product line, for example, uses a proprietary backplane and controllers that the company claims will equal or exceed the data throughput of systems using Ultra SCSI bus. "We don't give up anything to the SCSI and Fibre Channel arrays except the price," Ripley says. Other ATA-based RAID products, such as ExaDrive Networks' Diamond series, use a hybrid approach: They combine ATA disks with multiple SCSI or FC host interfaces and a proprietary controller.

According to the manufacturers, these ATA-based RAID products offer many of the same benefits as SCSI-based arrays. They typically support all standard RAID levels, including RAID 5, and they include hot-swap and hot-spare capabilities with automated failure detection, failover and data remirroring. They also provide policy-based management

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tools, remote monitoring and advanced diagnostics such as temperature, voltage and electrical current monitoring. Although ATA-based RAID vendors don't claim to match the largest enterprise RAID installations, some customers have built ATA-based network-attached storage systems using dozens of disks with 10TB.

ExaDrive Networks' Klein also noted that ExaDrive certifies the interoperability of its arrays with a variety of third-party products, including FC switches, storage virtualization, SAN management tools, and operating systems. "We approach the market differently than the big turnkey vendors. We say if you're looking for a best-of-breed approach, that's where we come in," he says. "The hardware savings give customers a margin to figure out where to get the best software solutions from high-end VARs and integrators. That's why we put a big emphasis on interoperability, especially on the Fibre Channel side for [storage area network] SAN implementations."

Serial ATA and iSCSI
Serial ATA (SATA), introduced in August 2001, offers several significant areas of improvement over ATA. The most noticeable improvement is data bandwidth: Serial ATA, which combines a new hardware interface with the existing ATA command protocol, supports data transfer rates up to 150MB/s - the next version of SATA will increase that to 300MB/s. SATA uses much smaller cables with a reduced pin count and a maximum length of one meter, allowing easier cable routing, improved system airflow and greater scalability. SATA also uses a lower operating voltage, as well as command queuing and other performance enhancements.

Some industry analysts believe that SATA could further close the already narrowing gap between ATA and SCSI disk drives. "I'd say that in the top 25% or 30% of the enterprise market, Fibre Channel drives will be the better choice," says Gartner's Roger Cox. "But from a technology point of view, the other 70% of the enterprise market could easily be satisfied by Serial ATA technology."

In order for SATA to make its mark on the enterprise market, however, major storage vendors will have to introduce products using the new standard and market them aggressively - something they have been slow to do. According to Cox, increasing competitive pressures will quickly force vendors to get serious about their SATA product plans. "I think someone like EMC coming out with a high-end network-attached storage product using Serial ATA would seize a tremendous breakout opportunity in this market," he says.

Another emerging standard, Internet SCSI (iSCSI), could further expand the reach of ATA-based storage in the enterprise. iSCSI, which specifies an IP-based networking standard for linking data storage facilities, could eventually challenge FC as a cost-effective solution for building storage area networks. "Serial ATA-based arrays, used in conjunction with iSCSI routers, storage switches and other products, could be a perfect match, especially in the midrange market," says Peter Gerr, research analyst for the Enterprise Storage Group.

ATA finds its niche - and more
So far, ATA-based RAID has received the warmest welcome in certain vertical markets. "Our major users include government and university research laboratories, oil and gas exploration, video surveillance, data storage and other customers who produce very large amounts of data," says Consensys' Ripley. "In many cases, there's no other affordable way to store that data without using tape or optical storage, and that means giving up immediate access to the data."

According to Scott Studham, group leader in the Pacific Northwest National Laboratory's molecular science computing facility in Richland, WA, the cost-performance relationship between ATA and SCSI was a decisive issue in the group's decision to invest heavily in ATA-based disk arrays. Studham says the laboratory recently migrated its supercomputer data archives from a 20TB tape-based system to an ATA-based storage array. In addition, he says the laboratory will use a 200TB ATA-based RAID array as primary storage for its new supercomputer, which he says will be the world's largest and fastest Linux-based system.

"A lot of people asked why we weren't using SCSI [RAID technology], but once I presented the facts, they all understood," Studham says, referring to the conclusions he reached about the performance and reliability of ATA-based disks vs. more expensive SCSI hardware. "In this environment, that 4% to 5% performance penalty for using ATA instead of SCSI doesn't outweigh the 200% to 300% price difference."

In the mainstream enterprise market, ATA-based RAID has also emerged as an alternative to tape-based backup systems and to nearline systems such as CD jukeboxes. As disk prices fall and ATA-based RAID products become more sophisticated, these products have created a new and rapidly-growing niche in the nearline storage market.

According to Jamie Riis, CIO of BayView Financial, a mortgage bank based in Miami, FL, moving to ATA-based nearline storage yielded significant benefits. BayView currently uses a Network Appliance NearStore R100 system to store backup data snapshots before moving them over to tape-based storage, allowing the company to provide almost instant access to recent backups. "It could take up to 20 hours to get this data from the tape system," Riis says. "Now if someone loses a file, we can go back at least to where they were at the last snapshot and restore the data in a few minutes."

In addition, Riis says BayView also plans to migrate its document image archives from an optical jukebox to the R100. "We'll go from a system where it takes 30 to 40 seconds to retrieve an image and we have to throttle user access, to an environment where hundreds of users are getting submillisecond access," he says.

According to Chris Bennett, director of product marketing for Network Appliance, Sunnyvale, CA, Riis' comments reflect an important trend for ATA-based enterprise storage: "ATA drive technology is enabling the industry to store information online that previously was not available," he says. "When you're comparing the amount of data now stored online to the amount stored on tapes stacked in cardboard boxes someplace, you're talking about orders of magnitude of difference."

Major vendors respond
Some top-tier vendors - such as IBM, Network Appliance, and EMC - have released ATA-based RAID products designed for nearline storage, disk-to-disk backup systems, or even as mainline storage for mid-market enterprise customers (see "Major vendors introduce ATA RAID products.")

Unlike their smaller competitors, these firms are more conservative about the short-term prospects for ATA-based RAID. "We don't yet see customers who are willing to put mission-critical data on ATA drives," Vaughn says. "You still get better performance with SCSI technology, and that performance advantage is clear. The ATA platform is important, but we're using it to target the midmarket and distributed environments right now."

Nevertheless, according to Bennett, Network Appliance was surprised by the response to its ATA-based NearStore product line, which began shipping in January 2002. "We've shifted significant resources onto NearStore because of the exceptional response," he says. "But we also want to position it where it's appropriate. It's not just a performance issue, it's an availability issue - the [ATA] drives are slower and more prone to failure, and you run a higher risk of degrading critical operations in an ATA environment."

This was first published in October 2002

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