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My motherboard currently supports both SATA II and III (3 Gb/s and 6Gb/s respectively), but after reading some online, it seems as though connecting a HDD to the 6 Gb/s is pretty much pointless. If this is the case I'm going to leave my two SATA III ports open for something that can actually use it (which at this point I'm not really sure what can).

This is part of an article I read:

In terms of everything else, we saw basically no difference from the same single drive being plugged into a SATA 6Gb/s or SATA 3Gb/s port. All of this is obviously due to the hard drive not being able to actually take advantage of the 6Gb/s bus.

from HardOPC.

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Well, i'd add though that you arn't going to lose anything from using a sata 3 port, and switching ports can be an option in future. – Journeyman Geek Jul 25 '12 at 3:07
up vote 32 down vote accepted

Things to keep in mind:

  • Due to 8b/10b encoding, the maximum data transfer rates of SATA II and SATA III are 300 MB/s and 600 MB/s, respectively.

  • When choosing a proper interface for a drive, the concepts fully utilizes and can benefit from are quite different.

    A drive with a maximum data transfer rate of 301 MB/s doesn't max out SATA III's 600 MB/s, but it will be limited by SATA II's 300 MB/s.

  • A drive's throughput (disk-to-computer transfer rate) is affected by both the internal (disk-to-buffer) and external (buffer-to-computer) transfer rate. The latter is determined by the interface (e.g. SATA III) and the drive, the former by the drive alone.

    The interface should always be slightly faster than the drive itself or it might slow the drive down.

My motherboard currently supports both SATA II and III (3 Gb/s and 6Gb/s respectively), but after reading some online, it seems as though connecting a HDD to the 6 Gb/s is pretty much pointless.

As of right now, the fastest HDD is the Western Digital VelociRaptor WD1000DHTZ: With a SATA III interface, its maximum external transfer rate is 401 MB/s (faster than SATA II). However, this is only significant when reading data that is already buffered or when using write acceleration.

The HDD's maximum throughput is 209 MB/s, which should not be slowed down by SATA II.

If this is the case I'm going to leave my two SATA III ports open for something that can actually use it (which at this point I'm not really sure what can).

Current consumer-level SDDs can certainly benefit from SATA III: For example, the Samsung 830 has a sequential reading speed of 520 MB/s, which would be severely slowed down by a SATA II interface.

When performing random reads, the interface's speed affects the throughput far beyond its rated limit:

random read performance

As you can see, none of the drives exceeds 200 MB/s with the SATA II interface; not even the Samsung 830 and OCZ Vertex 3 (SF-22XX), which pass 300 and 350 MB/s with the SATA III interface.

Furthermore, consumer-level SDDs could be much faster than even SATA III: For example, the PCIe SSD OCZ RevoDrive 3 has a maximum reading speed of 975 MB/s.

Enterprise SSDs achieve speeds far beyond SATA III's 600 MB/s: For example, the ioDrive Octal has a maximum reading speed of 6700 MB/s.

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This answer is perfect. Maybe I should in vest in an SSD at some point just for this reason. How can I test the max throughput on my hard-drive? I sure its under SATA II but I'm just curious. – nathpilland Jul 25 '12 at 16:56
One of the benchmarking tools Tom's Hardware used for the article Iometer, which is free and open source. – Dennis Jul 25 '12 at 17:04
Okay thanks so much – nathpilland Jul 25 '12 at 17:06
Please change "MB" to "Mb", there's also an order of magnitude difference between megabyte and megabit. – AaronLS Sep 4 '14 at 19:35
@AaronLS: Where exactly? – Dennis Sep 4 '14 at 19:37

No single HDD can fill a 6Gb/sec SATA link, nor a 3Gb/sec link.

If you use SSDs or port multipliers then it is a different story.

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+1 for port multipliers, I've never heard of these. I probably won't be using these, but it is an interesting consideration. – nathpilland Jul 24 '12 at 22:59

The majority of hard drives cannot fully utilize even SATA 1 interfaces.

Most 3.5" models (not above 7200 rpm) haven't even approached the 150 MB/sec limit at sequential reading. 2.5" 7200 rpm drives are even slower (usually under 100 MB/sec).

Sure, there are drive with 10000 rpm and 15000 rpm, but they are rare, expensive, noisy and more targeted at enterprise users than at home users. These high-performance hard drives saturate SATA 1.

Full SATA 2 speeds are unreachable for conventional HDDs for many years to come.

The only use for higher interface speeds would be the ability of a drive to transfer data from its buffer (usually 8 - 64 MB). Do you care about it?

Btw, SATA 3 is mostly useless even with many (but not all) SSDs. What gives speed and responsiveness with an SSD is its random read/write speeds, and they lie well below the SATA 2 threshold with many drives. Sequential read/write speeds, however, do exceed the SATA 2 threshold.

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-1 This answer is not accurate. SSDs can saturate any SATA III port. – Deltik Jul 24 '12 at 22:48

There is no mention here as far as i can see of the bottle neck at most motherboards sata 6gbs controller - whilst the hdd itself and the processor may support the quoted speeds of write and read, the motherboards onboard sata 3 controller in say an x58 board will not support these speeds at all.

When thinking of upgrading to ssd, remember that if the rest of your hardware is two or more years old you will probably not be able to achieve the highest speeds quoted as some of the older onboard controllers will not support such speeds. Higher speeds can be achieved by arranging drives in a raid array if your motherboard supports raid - but this may be a little too much for the average user to contemplate. In fact some users with older chipsets report faster speeds by using the sata 2 port instead of the earlier sata 3 ones.

To test the actually read write speeds of the ssd in your system you can use this link - there is a link here to the AS SSD Benchmark Test

pcie ssd's offer much higher performance figures as they bypass the slow controllers completely - their only downside is that bandwidth is split between your pcie slots so if you use a pc for graphic applications and have a high end graphics card the bandwidth will reduce for each slot - ie 2 x 16 pcie will reduce to 1 x 16 and 1 x 8. Another thing to bare in mind is that the motherboard needs to support boot from the pcie slot.if you plan to install your operating system on it.

When in doubt have a good look around for info before you commit your cash. i have always found to be one of the best sources of information when planning a build or upgrade, toms hardware and anantech offer good reviews and advice too.

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