Israeli start-up claims huge boost to SSD reliability

Israeli start-up claims huge boost to SSD reliability

Higher-endurance NAND will make SSDs more attractive for data center use

Israeli start-up Anobit Technologies Ltd. emerged from quiet mode today and announced its first product, a multilevel cell (MLC) solid-state drive that it says is as reliable as today's higher-end and higher-cost single-level cell (SLC) enterprise -class flash drives.

Anobit said its Genesis SSDs extend standard MLC endurance from about 3,000 to more than 50,000 write/erase cycles, an improvement of 20 times over the average consumer-class drive today -- making MLC technology suitable for high-duty cycle applications such as relational databases.

The drives come in 200GB or 400GB capacities with Serial ATA interfaces. Through the use of an external bridge, they are capable of using the serial-attached SCSI (SAS) or Fibre Channel protocol. The drives have a sustained sequential read rate of 220MB/sec. and a sustained sequential write rate of 180MB/sec., according to Anobit.

Anobit's Genesis series SSD

Anobit, which was founded in 2006 and has raised more than US$40 million in venture capital, said it has created a special processor, called a Memory Signal Processor, that boosts MLC NAND flash memory reliability through a special error-correction algorithm.

Gilad Engel, Anobit's vice president of business development, said the Memory Signal Processor adds an additional layer of error correction to the traditional error-correction code (ECC) that all SSD controllers have.

Engel said the 200GB Genesis SSD can handle 2TB worth of data writes per day for five years, and the 400GB SSD can sustain 4TB of writes per day. Both drives can achieve a write rate of 20,000 I/Os per second and a read rate of 30,000 IOPS, according to Engel.

The drives have native support for 512-, 520- and 528-byte block sizes and have a nonvolatile cache memory that's immune to power failures.

Engel would not offer any pricing for the drives, only saying that they would be "very competitive" with today's enterprise-class SLC SSDs.

According to Gregory Wong, an analyst at research firm Forward Insights, Anobit is not alone among SSD processor makers in producing technologies to extend MLC NAND's reliability. For example, Sandforce makes a processor that uses data compression and RAID architecture to get around the limitations of MLC.

Sandforce uses "24-bit/512-byte ECC hard coding. However, the fundamental issue is that the signal quality is declining, and Anobit's technology helps to get a 'cleaner' signal," Wong said.

The overhead for hardware-based signal decoding is relatively high, with some NAND flash vendors allocating up to 7.5% of the flash chip as spare area for ECC. Increasing the ECC hardware decoding capability not only increases the overhead further, but the effectiveness also declines with NAND's decreasing signal-to-noise ratio, Wong said.

Manufacturers over time have been able to shrink the geometric size of the circuitry that makes up NAND flash technology from 90 nanometers a few years ago to 25nm to 34nm today . The process of laying out the circuitry is known as lithography. Most manufacturers are using lithography processes in the 30nm-to-40nm range. Micron, Intel and Samsung are using 34nm, and Toshiba is using 32nm. Intel recently announced it has begun using a 25nm process.

The smaller the lithography process is, the more data can be fit on a single NAND flash chip. At 25nm, the cells in silicon are 3,000 times thinner than a strand of human hair. But as geometry shrinks, so too does the thickness of the walls that make up the cells that store bits of data. As the walls become thinner, more electrical interference, or "noise," can pass between them, becoming a tougher obstacle to tackle as it creates more data errors. The amount of noise compared to the data that can be read by a NAND flash controller is known as the signal-to-noise ratio.

In order to fix data errors, manufacturers include error-correction code in their NAND flash. The higher bit-error rates, the more ECC is required. Simply put, Anobit's processor is able to continue to read data for a longer period of time compared with typical NAND flash with hard-coded ECC, which takes up flash capacity.

Wong said Anobit is the first company to commercialize its signal-processing technology, which uses software in the controller to increase the signal-to-noise ratio, making it possible to continue reading data even as electrical interference increases.

"We believe that signal-processing technology such as Anobit's will be required for future generations of NAND flash memories, not just SSDs," Wong said.

Jim Handy, an analyst at Objective Analysis, said it makes sense that Anobit's proprietary technology would be able to offer dramatically lower prices than other SSD makers, because 70% of an SSDs manufacturing cost is in the creation of the NAND flash chips. Because MLC NAND can hold two to three times the capacity of SLC NAND in the same space, higher-capacity drives can be produced at a lower cost, Handy said.

"SLC NAND flash is becoming more and more of a niche product, so fewer and fewer companies are bothering to manufacture it because of the cost," Handy said.

Without naming which ones, Engel said some of the world's largest NAND manufacturers, consumer electronics vendors and storage array providers use Anobit's first-generation MSP technology in their products.

"Anobit is fielding orders from other well-known array vendors. All names you know well," said an Anobit spokesman, adding that "thousands of Genesis drives are already out for qualifications," and more will ship in the next couple of months.

MLC NAND flash has typically been used for consumer-class products, such as MP3 players and PC tablets, because it costs about four times less than SLC NAND flash, Handy said. The difference between the two nonvolatile memories is that SLC stores 1 bit of data per memory cell, while MLC stores 2 or 3 bits per cell, depending on the manufacturer. While MLC has greater storage densities, it also wears out faster.

Another way SSD manufacturers have dealt with MLC wear issues is through the use of wear-leveling software, which spreads writes out more evenly so that no one block of cells is worn out before another. But wear-leveling software is common to all SSD manufacturers.

Handy said he can see Anobit's MSP technology enabling manufacturers to use MLC more for higher-performance SSDs and thereby paving the way for lower-cost products in data centers.

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Tags storagesolid-state drivesisrael

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