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New processor technology promises big boost to consumer-grade SSDs

SandForce Inc. announced today a new family of solid-state disk (SSD) processors that the company claims will allow lower-cost, commodity NAND flash memory to be used in data center operations. The disks will also be faster and more reliable for use in mobile applications, the company said.

Saratoga, Calif.-based SandForce, which has been quietly working on the technology over the past three years, said its controller technology will allow multilayer cell (MLC) NAND flash memory to take the place of single-layer cell (SLC) memory in data centers, reducing the cost per gigabyte of capacity by three or four times.

SandForce said the SF-1000 SSD processor series, with its DuraClass firmware, will address the endurance, reliability and data retention issues associated with MLC NAND flash memory.

Jeff Janukowicz, an analyst at research firm IDC, said SandForce's new processor could be a major catalyst for increasing SSD adoption in the enterprise.

“These [kinds of] products should have a highly positive impact on efficiency and total cost of ownership when used in IT applications such as virtualization, transactional databases and automated financial trading — applications which can immediately benefit from the dramatic increase in performance and performance-per-watt that SSDs provide over [hard disk drives],” he said.

SLC NAND flash memory stores one bit per cell, enabling it to natively offer much higher read/write speeds than MLC as well as up to 100,000 write cycles per solid-state disk drive, compared with 2,000 to 10,000 write cycles for MLC memory. MLC memory stores two or more bits per cell, which offers higher capacity, but requires more complicated firmware to automate the reallocation of data throughout the drive as it is stored and erased.

SSD is a recent phenomenon in enterprises that allows greater throughput for I/O intensive applications, such as relational databases. Corporations adopting SSD as a “tier zero” level of storage in their storage-area networks (SAN) above high-end Fibre Channel and serial-attached SCSI (SAS) hard disk drives, have only trusted SLC SSD. Because of its lower price and higher capacity, MLC SSD has been popular for consumer-type applications, such as mobile computing and USB flash drives.

Resellers such as IBM and EMC Corp. have been adding SSD to their high-end arrays in recent months.

Mike Desens, IBM's vice president for system design, said SandForce's SF-1000 SSD processor family promises to offer MLC SSD that can be reliably used in mission-critical storage environments.

“These innovations can be truly disruptive and will accelerate the adoption of solid-state technologies across the data center,” Desens said.

Part of the problem with SSD has been its write performance. SSD has fixed data block sizes, so that if a system writes a 4k block of data to a drive, as much as 128k of capacity may be used to store the data. The problem is known as write amplification. To address the problem, manufacturers use firmware to redistribute data more evenly across the media, a process known as wear leveling. Write amplification accounts not only for the disparity between random write and read speeds on SSD, but also the endurance of the media, which wears out faster because of the additional data writes required in the reallocation process. Manufacturers, such as Intel Corp., have added DRAM buffers to their SSD drives as short-term memory in order to speed up random writes.

SSD manufacturers often advise users in their product manuals to limit writes per day in order to extend the life of the drives, and users exceeding those limits void product warranties.

SandForce said a function in its DuraClass firmware, called DuraWrite, optimizes writes, thereby reducing the number of them and improving SSD media endurance by up to 80 times, allowing unlimited writes to the disk. The company also claims its controller can improve MLC sequential read/writes to 250MB/sec. or 30,000 I/Os per second using 4k random writes.

Another technology SandForce has added to its controller is called RAISE, or redundant array of independent silicon elements, which it said acts like RAID in striping data across NAND flash chips to improve failure rates.

Kent Smith, senior director of product marketing at SandForce, would not reveal technical details behind the company's firmware, but he said that RAISE increases the reliability of an SSD by 100 times. For example, a typical SSD chip contains eight dies or silicon wafers capable of storing up to 32Gbits of data. In every SSD drive, there can be as many as 128 dies for a total capacity of 512GB.

The failure rate for 128 dies is 12% over the lifetime of an SSD, according to Smith, or 1,000 parts per million. “With RAISE, we can recover, even if a complete die fails, or up to 32Gbits of data can fail and we can recreate it,” Smith said.

Because of the SF-1000 SSD processor's greater efficiency and write reduction, Smith said power efficiency is also markedly increased on SSDs — up to 5,000 I/O per second per watt.

Prior to founding SandForce in 2006, CEO Alex Naqvi had been the senior architect for Nvidia Corp.'s graphics processors, and prior to that, he held senior engineering and architect positions at Nishan Systems, Toshiba and Gizmo Technologies.

SandForce will be targeting SSD manufacturers, such as Micron Corp. and STEC Inc., with its new SF-1000 processor, which will be available at the end of April.

“Our team has a deep understanding of both system- and silicon-level issues to strike the right balance of performance, power, cost and time-to-market in SSD processor products,” Naqvi said. “By looking across all of the flash vendors' products and road maps, we have been able to think out-of-the-box to provide an optimal solution that supports multiple vendors.”

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