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SSDs not yet ripe for 'storage-class' apps

Posted: 03 Sep 2008 ?? ?Print Version ?Bookmark and Share

Keywords:solid state drive? SSD? storage-class apps? NAND flash?

Solid-state drives (SSDs) are promising, but an analyst believes that the technology may not be ready for prime time in higher-end enterprise or "storage-class" applications.

For these high-end, "storage-class" applications, NAND-based SSDs could hit the wall. Instead of using NAND, phase-change and resistive memory technology looks more promising in storage devices, said Bob Merritt, an analyst with Convergent Semiconductors, a research firm.

Right market
Based on NAND flash memory, SSDs are supposed to replace hard drives in select applications, such a mobile PCs, notebooks and enterprise servers. But SSDs are still more expensive than hard drives and the price delta between the two technologies remains wide.

Still, the market is just taking off. SSDs are now appearing in ultra mobile PCs, high-end notebooks and servers.

"In the past, we were dealing with magnetic media, DRAM, and SRAM when we stored data. All of those technologies are assumed to have no wearout mechanism relative to writing and erasing data and therefore an infinite level of erase and rewrite cycles," Merritt said.

"However, there is a known wearout mechanism for NAND. SLC wearout is measured in tens of thousands, and MLC is in thousands. So now we have to carefully consider the performance requirements of the application before we decide if SSD is appropriate," he said.

"OEMs are therefore identifying applications that do not require a lot of erase and re-write cycles from the higher level of performance that people are starting to call 'enterprise class.' NAND SSD can adequately support that first class of applications," he said.

Some companies, reportedly including IBM Corp. and SanDisk Corp., "do not believe that NAND is capable of supporting higher reliability enterprise class" SSD applications, he said.

To position SSDs in these segments is a mistake. "SSDs are a product with significant positive impact and tremendous high-volume potential. The risk to the semiconductor companies is that an OEMor most likely an end usermay in fact allow SSDs into an application for which it was not the appropriate technology, and the resulting backlash is that SSDs are 'unreliable,' " he said. "I think it is premature for semiconductor companies to completely hand off the responsibility of maintaining the integrity of the technology."

The answer? SSDs are ideal for some but not all applications. For the high-end enterprise, NAND flash-based SSDs won't cut it.

IBM, and to some degree, SanDisk, believe that "phase-change and resistive memory will be the only two (technologies) that look commercially viable," he said.

IBM calls resistive memories as "solid electrolyte" or "SE memory." The only known IP sources of SE memory are Hewlett-Packard Co.'s memresistor technology and the Arizona State/Axon Technology memory, he added.

Dawn of memristors, PMC
Memristors, the fourth passive circuit in electronic circuit theory, have moved a step closer to prototyping with the harnessing of a substrate material that could yield a new memory device by 2009.

In April, HP Labs claimed to have "discovered" memristors. Now, HP Labs said it has demonstrated how to control its memristor material, which changes resistance in response to current flowing through it. The advance promises to speed development of commercial prototype chips for its RRAM (resistive random-access memory) by next year.

Meanwhile, Axon Technologies Corp. is devising what it calls a Programmable Metallization Cell (PMC) memory device. PMC is a resistance-change, non-volatile memory technology that features a significantly lower power profile than conventional devices, such as flash. PMC is considered ideal for a broad range of applications, including energy-saving computing, personal entertainment and mobile communications.

PMC was developed at Arizona State University. Axon's non-volatile memory technology is being licensed for both discrete memory and embedded memory applications.

- Mark LaPedus
EE Times

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