[International] Serial ATA, PCIe converge for flash drives


SAN JOSE, Calif. – The serial ATA interconnect will take a ride on PCI Express to support data rates of 8 and 16 Gbit/second to serve the accelerating needs of sold-state and hybrid drives. The move is a sign of the rising proliferation of both flash drives and PCIe.


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 3 Gbit/second 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.


SATA Express will handle up to two lanes of PCI Express to deliver 8 Gbits/second when implemented with PCIe Gen 2 or 16 Gbits/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, said 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," said Huffman.


Flash drives are on the rise and increasingly adopting PCIe.


Objective Analysis (Los Gatos, Calif.) 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 Fibre 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.


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


Source: EETimes