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And the Sign of the Beast is 6 (Gbps that is)

Jan 07, 2010, 07:33 (0 Talkback[s])
(Other stories by Jeffrey B. Layton)


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"The two primary interface standards for storage devices are SATA (Serial Advanced Technology Attachment) and SAS (Serial Attached SCSI). Both have been around for a number of years, SATA first appearing in 2003 and SAS appearing in 2004. Also, both of them have similar throughput performance currently at 3 Gbps (SATA started at 1.5 Gbps while SAS started at 3.0 Gbps). However, lately both protocols had been showing their age, particularly with the advent of SSD (Solid State Drives). However, the committees that oversee the protocols have not been idle and have created the next generation for each protocol - 6 Gbps.

"Who needs 6 Gbps?

"Hard drives are increasing in throughput performance but at a rather slow rate meaning that the performance of a single hard drive hasn’t changed all that much in recent years. While perhaps not the best source of benchmarks and testing, Toms Hardware did run a very interesting article that examined desktop hard drives from the last 15 years. It is a very nice retrospective of how hard drives have changed ending in 2006. In particular, this chart shows that the performance of a single SATA drive in 2006 was about 64 MB/s. The performance of single hard drives today are about the same. So if individual drive performance is somewhat stagnant, why do we need a faster storage interface? The answer is fairly simple - either we have multiple drives attached to a single interface (i.e. RAID) or we are using SSD’s (Solid-State Drives) or a combination.

"The stated throughput of either a current SAS or SATA controller is 3 Gbps. A 3 Gbps interface has a theoretical throughput of 375 MB/s (Mega-Bytes per second) but actual throughput is a bit lower than that. Internal to the storage system there is data and handshaking processes taking place that reduce throughput. Also, the data is transmitted in packets (sort of like a network) that can also reduce throughput. The ASIC on the controller as well as the details of the drive performance itself can also affect performance. A rule of thumb for the 3 Gbps interface is that the maximum throughput is about 275-300 MB/s."

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