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PCIe, SATA combine for next-gen flash drives

Posted: 11 Aug 2011 ?? ?Print Version ?Bookmark and Share

Keywords:flash drives? PCIe? serial ATA?

To support further support and address the accelerating needs of solid-state and hybrid drives, the serial ATA interconnect will collaborate with PCI Express technology. The move is believed to be a sign of the rising proliferation of both PCIe and flash drives.

The Serial ATA International Organization (SATA-IO) will create a so-called SATA Express standard as part of its version 3.2 specifications expected out by the end of the year. The spec essentially ports serial ATA software to the PCI Express transport and defines new connectors needed for cards and drives that use it.

Many early flash drives adopted 3Gb/s SATA because it was fast enough, low cost and widely supported in PCs. But with the advent of new, faster NAND flash interfaces the SATA "host interface has become the bottleneck," said Mladen Luksic, president of SATA-IO and an interface engineer at hard drive maker Western Digital.

PCIe dominance
Objective Analysis forecasts PCIe will become dominant in server SSDs in 2012, with unit shipments greater than the combined shipments of its Serial-attached SCSI (SAS) and Fiber Channel drives. By 2015, the market watcher predicts more than two million PCIe SSDs will ship, more than all of the SATA SSDs sold in 2010.

SATA Express will handle up to two lanes of PCI Express to deliver 8Gb/s when implemented with PCIe Gen 2 or 16Gb/s with PCIe Gen 3. The newly minted 8 GTransfers/s PCIe Gen 3 interface will begin shipping in volume in PC products over the next six months, says Amber Huffman, a technical lead at SATA-IO and a principal engineer in Intel's storage group.

Current SATA interfaces are usually implemented in PC chip sets and device SoCs using an embedded controller to support the Advanced Host Controller Interface. SATA Express will allow devices to tap directly into PCI Express links coming off chip interfaces and even some modern processors.

The low latency, particularly of the CPU links "makes it a very interesting interface for solid-state drives," Luksic said.

Flash drives are on the rise and increasingly adopting PCIe.

Serial ATA is used in the vast majority of notebook and desktop hard drives, but less than a third of server drives, territory owned by the more robust and higher cost SAS interface.

SAS specialists such as LSI Corp. are already showing 12Gb/s SAS chips, but industry efforts also are also underway to port SAS to PCI Express. Specs for a so-called SCSI over PCI Express standard are not expected to be finished for about a year.

The existing 6Gb/s serial ATA interface adequately serves a wide range of desktop, notebook and consumer systems, says Luksic. The SATA-IO group will explore needs for those systems as they evolve in the future, he says.

- Rick Merritt
??EE Times

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