Hitachi Global Storage Technology (HGST), which was recently acquired by Western Digital, claims to be first with a demonstration of the first 12Gb/s SAS SSD. The company will be unveiling the device at the SCSI Trade Association Technology Showcase, which take place in Santa Clara on May 9.
As the name indicates, the drive is theoretically capable of transferring data at 12 Gb/s - twice the rate of current 6 Gb/s drives - which translates to a total bandwidth of 4.8 GB/s.
“We have successfully achieved interoperability between our 12Gb/s SAS drive and 12Gb/s SAS HBAs and expanders from both LSI and PMC-Sierra,” said Brendan Collins, vice president of HGST product marketing, in a prepared statement. “Meeting these interoperability milestones is critical when preparing the industry for the adoption of a new interface standard."
HGST said that it expects market adoption of 12 Gb SAS drives in 2013.
Gb/s is not the same as GB/s
As is typically the case with news bits here, this is woefully short on details or expected further explanations.
Peak performance of 6Gb/s SAS is actually 24Gb/s using link aggragation which basically bundles 4 ports together. Like other current serial interfaces (SATA/USB), for every 10bit packet, 8bits are actually data. So out of the theoretical bus transfer limit of 3GB/s, 2.4GB/s would be the usable data transfer rate. Just double this to get the 4.8GB/s rate quoted in this article for the new 12Gb/s SAS standard.
SATA and SAS have the exact same bandwidths. So, if this is an SAS or a SATA 12Gb/s device, it means that at best, it can transfer at 1.2GB/s. In order for it to have 4.8GB/s, it would need at least four SATA/SAS 12Gb/s ports.
So yes blazorthon, you're right. Another example of an interface that uses 8/10 encoding is PCIe, that is up until the PCIe 3.0 specification which has a 128/130 bit encoding. IE, a PCIe 2.0 lane has a 5Gb/s connection between the two devices on either end, but only 4Gb/s is actually usable for transferring data between either side because the extra 1Gb/s is used for error correction in the data. PCIe has an 8Gb/s connection, but it's change to a 128/130 bit encoding allows it to have an almost double the bandwidth of PCIe 2.x.
Yet another common interface that uses 8/10 is USB.