A lead from Computerworld put me onto the announcement by SMART Storage Systems of a new enterprise-class Optimus Ultra SSD based on consumer-grade MLC (multi-level cell) NAND Flash devices. Using consumer-grade silicon to make this drive cuts the OEM cost per Gbyte by about half, so there’s real incentive to come up with something very clever to enable this design approach.
Enterprise-class storage requires more data reliability under harder use than consumer-grade NAND Flash is designed to accommodate, so making a high-grade SSD from lesser-grade NAND Flash is an interesting exercise in system development. As the Computerworld article says, consumer-grade MLC NAND Flash chips are rated for perhaps 3000 program/erase cycles and that sort of raw endurance would be fatal for an enterprise-class SSD. The new Optimus Ultra SSD from SMART Storage has an endurance rating of 100,000 program/erase cycles, so something pretty interesting is going on inside of the box.
The Computerworld article say this about the way SMART Storage boosts drive endurance:
“SMART Storage achieves its NAND flash endurance through a combination of aggregated flash management and signal processing techniques. Aggregated flash management combines writes to reduce wear and signal processing increases the signal-to-noise ratio, making it possible to continue reading data even as electrical interference rises as electrons leak between flash cells.”
Write combining to reduce the number of write-erase cycles is a well-known technique. Any good SSD controller should be able to support that, although there are clever ways to do it and then there are ways that are even more clever. However, what’s this stuff about signal processing? How do you get at the information needed to evaluate cells inside of a NAND Flash device?
I checked with the SMART Storage Web site to seek more illumination and found this video on the Company’s so-called Guardian Technology:
And then I found this article on the StorageReview.com site. The article explains that SMART Storage System’s Guardian Technology consists of three component technologies. The first, called FlashGuard, intelligently manages the Flash media. It maximizes the use of “stronger” Flash cells and minimizes the use of weaker cells. A key characteristic of Flash memory devices is that some cells do have less endurance and those weaker cells set the endurance spec for the entire Flash chip if all of the on-chip cells are treated equally. SMART Storage has figured out how to detect, map, and isolate these weaker cells at manufacturing time to increase system endurance. FlashGuard also employs a proprietary ECC algorithm to further boost data integrity.
The second endurance-boosting component technology in the Guardian triad is called DataGuard, which combines data-path protection, ANSI T10 DIF (data integrity field) protection blocks (just like the big boys use), and cross-die redundancy.
The third component technology is called EverGuard, which appears to be an internal power-backup technology based on capacitive energy storage, coupled with some architectural features that manage internal drive power more effectively to ensure that scheduled writes can occur even when system power is lost.
Together, these technologies telegraph a truth in the SSD market. It’s not going to be possible to just slap an SSD together using standard NAND Flash memories, an off-the-shelf controller chip, and some vendor’s standard SSD firmware and hope to compete for high-margin opportunities. SMART Storage has obviously put a lot of thought into the design of the Optimus Ultra SSD to make it stand out in a market that becomes more crowded by the day.
How will your SSD development team do the same?