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MLC drives, PCIe technology give SSDs run for their money

Manufacturers see demand grow for multi-level cell (MLC) solid-state drives and PCI Express technology to bring down prices.

IT managers turned off by the high price of solid-state storage might want to take another look now that manufacturers are escalating production of lower-cost multi-level cell (MLC) drives and new MLC-based PCI Express (PCIe) technology to meet the demands of their enterprise server and storage system customers.

Research from Framingham, Mass.-based IDC shows that MLC NAND flash accounted for only 27% of the enterprise solid-state drive (SSD) revenue last year. But the market research firm predicts MLC revenue will rise to 52% next year and hit 60% in 2013.

Jeff Janukowicz, IDC’s research manager for solid-state storage, attributed the surge in MLC interest to the more than 50% price discount vs. the single-level cell (SLC) drives that dominate enterprise solid-state shipments plus advancements in controller technology that have improved MLC performance and endurance.

“Today’s MLC drives really are enterprise-class solutions,” Janukowicz said, “and they’ll provide that 24/7 performance and reliability that many of the traditional enterprise storage vendors are looking for.”

IBM is already moving to MLC and enterprise MLC (eMLC) on its storage arrays and servers whenever possible, according to Andy Walls, a distinguished engineer in the company’s storage hardware architecture division. The company’s System x servers are more than half SLC, but MLC is on the rise, he noted. He said a 200 GB eMLC SSD for System x that has shipped since late in the second quarter is “very popular.” He added that most of IBM’s sales of Fusion-io Inc. PCIe SSDs are MLC, and the rest are SLC.

Walls said IBM sells mostly eMLC with its Power Systems, and the storage division favors eMLC, too. IBM’s Storwize V7000 midrange disk system, for instance, supports 300 GB 2.5-inch eMLC SSDs.

“Our customers want to use SSDs but need affordable solutions. MLC and eMLC are an important part of that affordability,” Walls said via an email interview. “I would expect the mix of eMLC will grow with SLC decreasing. MLC will probably stay the same.”

One of the main distinctions between SLC, eMLC and MLC is endurance. All the bits in a NAND flash block must be erased before any data can be written, or programmed, and the program/erase process eventually breaks down the oxide layer that traps the electrons, and NAND flash wears out.

Wear-out predictions vary widely by manufacturer, but the most commonly cited figure for SLC NAND flash is 100,000 program/erase cycles, which are also known as endurance or write/erase cycles. For eMLC, it’s roughly 30,000; for MLC, it can be 10,000 or less.

“The drive makers have found ways to get past MLC’s limited endurance,” said Jim Handy, chief analyst at Objective Analysis in Los Gatos, Calif., pointing to mechanisms such as “a smart algorithm that figures out when a block is wearing out” and overprovisioning a system with more flash than it requires.

Enterprise drive makers such as Hitachi Global Storage Technologies (GST) (whose acquisition by Western Digital Corp. has yet to finalize), SMART Modular Technologies Inc. and STEC Inc. now promise MLC/eMLC drives capable of 10 full-disk capacity writes per day for five years.

Hitachi’s new eMLC-based Ultrastar SSD400M 400 GB claims to deliver 7.3 PB of lifetime random writes, or 4 TB/day for five years vs. the 35 PB with SLC, according to Ulrich Hansen, director of market development at Hitachi GST. Hansen estimated that 90% of the enterprise SSD world (excluding SATA-based SSDs) is SLC today, but he expects the volume to shift to 70% MLC within two years.

XIO, formerly known as Xiotech Corp., went with SMART Modular’s eMLC approximately 18 months ago after its research showed the algorithms for wear leveling and the drives’ life expectancy had improved significantly, chief technology officer Steve Sicola said. XIO’s Hyper ISE algorithms also reduce the write cycles and, in turn, the stress on the drives, he added.

Satisfied that the technology is now reliable enough, Texas Memory Systems Inc. joined the eMLC bandwagon with its RamSan-810. If users write at 600 MBps, the RamSan-810 can write 10 TB five times per day. The $13/GB for the eMLC-based RamSan-810 will roughly halve the $25/GB street price of the SLC-based RamSan-710, according to company officials.

Major data storage vendors that have used only SLC drives to date are also becoming receptive to MLC/eMLC SSDs. In May 2011, EMC Corp. announced plans to design, test and qualify MLC-based SSDs for enterprise-class applications and incorporate them into EMC systems later this year.

“SLC will continue to be required for solutions that require high write reliability such as caching technologies,” said Barry Ader, senior director of storage product management in EMC’s flash business unit, in an email interview. “We do see the MLC growing as well and having a place in the enterprise as the technology becomes more resilient.”

Dell Inc. added MLC drives from SanDisk (with technology acquired from Pliant Technology) in its EqualLogic PS6100 storage arrays launched this month.

The sweet spot for MLC tends to be read-intensive workloads with limited write needs, such as Web content hosting, video streaming and booting drives in servers. eBay has deployed 100 TB of Nimbus Data Systems Inc.’s S-class solid-state storage, equipped with SSDs from Micron Technology Inc.

MLC also makes its mark on PCIe

PCIe pioneer Fusion-io claims the vast majority of its more than 22 PB of customer deployments have featured MLC products. The company professes to have more than 1,500 enterprise customers, including financial institutions such as Credit Suisse and NYSE, and social networking sites such as Facebook.

One sign that PCIe is picking up steam is the growing number of competitors that Fusion-io has acquired. The list now includes LSI Corp., Micron, OCZ Technology Group Inc. and STEC, which announced a PCIe option earlier this month. Intel Corp. also plans to add PCIe flash “at some point,” according to Troy Winslow, director of product marketing in the company’s Non-volatile Memory Solutions Group.

“It’s an exciting time in the marketplace. Fusion-io has beaten a path, and now everybody else is chasing down that path trying to take away some of Fusion-io’s market,” Objective Analysis’ Handy said. “But that’s probably a good thing for them because it’s going to become a very large market.”

According to Handy’s market statistics, PCIe enterprise SSD unit shipments will more than triple from 74,300 this year to 227,600 next year. By 2014, PCIe-based SSDs will exceed SAS SSDs, 2.25 million units to 1.84 million units, according to his forecast.

IDC’s market research shows that 13% of the SSD units that shipped last year leveraged the PCIe interface rather than traditional storage interfaces such as SAS, SATA and Fibre Channel. By next year, IDC expects the PCIe volume to increase to 19% and then 25% by 2014.

Most often found in servers, PCIe-based solid-state options can boost performance and lower latency because the drive can be connected directly to the PCIe bus, bypassing the traditional storage protocol overhead. Examples of PCIe-based products include NetApp’s Flash Cache and Oracle Corp.’s Exadata.

One prominent new PCIe entrant on the horizon is EMC’s PCIe/flash-based server cache techpcirnology, code named Project Lightning, which is due later this year. IBM also expects to continue to grow its use of PCIe-based storage, according to the firm’s Walls.

Prime use cases for PCIe include I/O-intensive applications such as social networking, Web serving, Web hosting, online transaction processing, data warehousing and busy databases.

“In social networking applications, they can’t serve up the data fast enough,” said James Bagley, a senior analyst and business development consultant at Storage Strategies Now in Austin, Texas. “These PCIe boards were just a godsend to them. They could pop them in their heavyweight virtualized servers, speed up their workloads and in many cases take the load off their shared storage.”


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