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SATA   SATAIII - what does it mean for me

    Rick Stephens

  Spring/Summer 2010 - Talk of SATAIII is creeping into the awareness of 'cool' new stuff happening. SATAIII hype, and even SATAIII products, are starting to show up in advertisements and marketing lingo. This short article is an attempt to put into perspective how soon we can expect SATAIII to make a difference in our storage capabilities and how it will effect our purchasing decisions.



   SATAIII is a new bus specification designed mainly for hard drives, but also intended for use by other devices like optical drives and Solid State Storage Devices. SATAIII is also called SATA 6Gb and SATA600 (6 Gigabit/sec and 600 MegaByte/sec being the same number written two different ways). SATAIII sets targets for the industry to allow growth in performance and capabilities of the SATA bus and its attachable devices while maintaining compatibility across the industry.

  While there are other functions and features added to each new specification, like port multiplication coming out in SATAII spec, most of the talk is centered around the increase in maximum bus throughput. Marketing tends to stress only the bus speed, seldom mentioning other features and changes to the specification. The established performance targets for each of the SATA specifications are:


 SATAI   - 150 MB/sec - 1.5 Gb/sec
 SATAII  - 300 MB/sec -  3 Gb/sec
 SATAIII - 600 MB/sec -  6 Gb/sec

  Real life performance/throughput on a given bus is less than the stated bus speed. The bus target speed is a goal never reached. For instance, the fastest I have ever seen pushed through a SATAII bus is 230 MB/sec connected to an SSD.



  All SATA buses have the primary design criteria of maximizing the performance of hard drives with spinning disks. Operationally, especially in timing of data transfers, a hard drive is a much different type of mechanism than a Solid State Device that is composed all of memory chips.

   Current hard drive 'state of the art' has the typical drive's maximum mechanical speed, which is based on the head's capability to read the platter as it spins by, at roughly 125 MB/sec. Reality is, because the drives are only capable of 125 MB/sec, increasing the bus speeds to 600 MB/sec from 300 MB/sec SATAII bus is going to have no real effect whatsoever.

   Yes, there will be some small gain in performance for very small accesses, those small enough to be contained within the cache on the drive. But until we see a big increase in platter to head performance of drive mechanisms, or a change in the type of media used, almost no performance benefit will be given to a single hard drive just by virtue of increasing the bus speed to 600 MB/sec.


Port Multiplier Storage

  Port Multiplication is where we'll really see the big performance benefits from SATAIII! A RAID on current SATAII Port Multiplier bus is limited to around 230 MB/sec per single cable or port on a SATA host card. This limit is the maximum speed we have seen through a single SATAII port under any configuration (not quite the 300 MB/sec advertised for SATAII buses). With the introduction of SATAIII we should experience a doubling of that performance (from 230 to nearly 450 MB/sec) on a set of drives attached to a single port multiplier.

  Today we need 2 port multiplier boards and 2 connections to achieve throughputs of over 230 MB/sec. Tomorrow, with a SATAIII bus and SATAIII port multiplier boards, we will be able to double that to nearer 450 MB/sec for a single eSATA cable.

   This will be a significant improvement to storage performance. But it also will require that not only is the host card SATAIII specification with eSATA ports capable of supporting port multiplication at SATAIII speeds - but also one piece of the puzzle not yet even being talked about: SATAIII port multiplier boards. Until they come available this is all just hopeful talk. I have yet to hear of any progress being made towards design and release of a SATAIII port multiplier chipset. We keep asking though.


Solid State Storage

  The one place we will see performance gains right now with SATAIII buses will be in the use of Solid State Storage Devices (SSDs). SSDs work at RAM speed. High end SSDs can easily top 600 MB/sec. Hooking up a high end, and high dollar, SSD to your SATAII bus will give real performance in the neighborhood of 230 MB/sec. Doing the same on a SATAIII bus should immediately double that!

  The SATA bus is designed for spinning mechanical hard drives, not SSDs. We won't see the type of throughput that SSDs are capable of until we have a bus designed to use the speed of a memory chip instead of a bus designed for spinning disk hard drives. But until that day, a faster SATA bus is a welcome improvement.

   While I haven't seen much testing of high end SSD drives on SATAIII buses yet, I expect that when developers start rolling out SATAIII host cards, soon after will arrive a whole bunch of choices in SATAIII compatible SSDs. 450-500 MB/sec storage is going to make a HUGE dent in the slowest process in today's computers, getting the data off a hard drive is like crawling on hands and knees in the 100 yard dash compared to all the other solid state processes happening in the computer.

   It is going to make a big difference in the cost analysis on whether to buy an SSD for your boot or work drive when we can enjoy these kinds of speeds. 450-500 MB/sec is 4 times the speed of a current mechanical hard drive and twice as fast as current SSD's on SATAII buses. With these kinds of numbers it starts to make sense to spend the money on solid state.



  SATAIII is not yet a big factor in our storage buying choices. Only when we have all the pieces available, with SATAIII drives, buses, bridges, SSDs and port multipliers, will an advantage be realized. In the meantime keep an eye out for improvements in SSD performance based on SATAIII. I expect many more offerings of SATAIII solid state storage based on SATAIII performance improvements. This will lead to cost reductions for the consumer.


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