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.
What is SATAIII
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.
Performance
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.
Conclusion
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.
The Gurus Certify This Guide Rules!
