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Cheaper MLC NAND flash drives poised to drive enterprise SSD adoption

Carol Sliwa, Features Writer

Enterprise adoption of solid-state storage has been tepid, but that could start to change next year as automated tiering software and less expensive multi-level cell NAND flash (MLC NAND flash)

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solid-state drives (SSDs) increasingly make their way into storage systems.

Nearly 60% of the 159 IT professionals who responded to a fall purchasing intention survey conducted by SearchStorage.com and Storage magazine, said they haven't implemented SSDs because they're too expensive.

So far, most of the enterprise data storage systems shipping with SSDs have used single-level cell NAND flash (SLC NAND flash) technology. The SLC chips cost approximately five times more per GB than MLC chips, said Jim Handy, founder and SSD analyst at Los Gatos, Calif.-based Objective Analysis.

But SLC flash is superior to MLC in the areas of endurance, reliability and performance (especially on writes). To make MLC sufficient for the enterprise, drive manufacturers have had to improve the technology to mitigate the drawbacks and gain acceptance from the enterprise storage vendors that need to stand behind their products. IBM is sold on MLC, and is replacing SLC drives with STEC Inc.'s ZeusIOPS MLC SSD on the IBM DS8700, DS8800 and Storwize V7000 storage arrays. An IBM spokesperson said it sells only MLC SSDs on those systems because the cost per gigabyte is too high for SLC.

"The migration of enterprise SSD to MLC is inevitable," Handy predicted. "Although it looks challenging and worrisome today, as controllers become more sophisticated, it will become a very acceptable thing, and it will be proven to be sufficiently reliable for any enterprise application."

Scott Shadley, STEC's manager of SSD technical marketing, said he expects more of STEC's OEM partners to use MLC, which he said is at least 25% less expensive than SLC flash. STEC said its use of adaptive flash access, signal processing, data management algorithms and error correcting code (ECC) help improve the endurance of the MLC flash components.

MLC tip: Know your writes

Dan Marriott, director of operations at Answers.com, said his company has used MLC-based SSDs in its primary database servers for more than 18 months. Answers.com uses MLC and SLC Hewlett-Packard StorageWorks IO Accelerator cards (from Fusion-io) in BladeSystem servers.

But Marriott added that it's imperative to know the expected lifetime writes of the SSD, to measure the average and maximum number of writes that an application makes to SSDs and to monitor SSD health.

Marriott wrote in an e-mail that his company has more than 99% reads vs. writes, "below any danger threshold." He determined that the expected MLC-based SSD lifetime was within an acceptable range, even taking into account anticipated application growth.

Joseph Unsworth, a research director who tracks NAND flash semiconductors at Gartner Inc., said MLC technology has benefitted from better controllers and firmware, and should make up most of enterprise SSDs by 2012.

"It's the best way to cut prices considerably, as long as there's minimal compromise on quality, of course," he wrote in an e-mail interview.

Automated tiering clears another SSD hurdle

Industry analysts predict that solid-state usage will increasingly go hand in hand with automated tiering technology that shifts the most active or I/O-intensive data to more expensive SSDs and less important data to high-capacity SATA or other cheaper hard disk drives (HDDs).

Compellent Technologies Inc., which was recently acquired by Dell Inc., pioneered the use of block-level automated tiering, and its storage systems can shift data in page sizes of 512 K, 2 MB or 4 MB based on the customer's needs. Larger vendors promoting automated tiering in connection with SSDs include IBM, with its IBM Easy Tier technology, and EMC Corp., with its FAST technology in Symmetrix V-Max, Clariion midrange systems and Celerra NAS boxes.

Distinguishing features between the different vendors' automated tiering offerings include the level of granularity at which the data moves between tiers, the degree of automation the system affords and the extent to which users can define policies for shifting data.

"When you do automated tiering, it's like managing your real estate. You make sure your SSDs are always fully used," said Valdis Filks, a research director for storage technologies and strategies at Gartner. "If you use SSDs as point solutions, you may not be getting the most out of them, so automated tiering increases the payback for SSDs. When you automate the usage of them, the busiest data is always there."

While automated tiering may appeal to some administrators, others are hesitant to relinquish control. For instance, Olivier Parcollet, director of systems information at the private company that operates the public transportation network for the city of Orleans, France, Société d'Exploitation pour les Transports de l'Agglomération Orléanaise (SETAO), has concerns that automated tiering might place unimportant data onto his expensive SSDs.

"I don't like the storage automatically moving blocks of data from one tier to another because it's not predictable," said Parcollet, whose company uses Pillar Data Systems Inc.'s Axiom storage arrays with SSDs.

However, Mark Peters, a senior analyst at Milford, Mass.-based Enterprise Strategy Group, said automated tiering becomes more appealing in combination with the cheaper MLC-based drives.

"It's now cheaper and easier to use," Peters said. "All by itself, the emergence of MLC for the enterprise would help solid-state adoption. But in combination with automated hierarchical storage management, it will be a double acceleration."

This article was originally published on SearchStorage.com.

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