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I purchased a Baraccuda hard-drive (model ST3000DM001) that supports a maximum read transfer rate of 210 MB/s and SATA 1.5/3/6 Gb/s. My motherboard has a limited number of 6 Gb/s ports so I'd like to reserve them for when it's really necessary.

When does a hard-drive benefit from a SATA 6 Gb/s port? Doesn't it require a transfer speed of at least 375 MB/s to surpass the limit of SATA 3 Gb/s? Are there any other benefits of SATA 6 Gb/s vs 3 Gb/s ports?

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A hard drive benefits from being connected to a 6Gbps SATA port when the drive is capable of sustained transfers faster than a 3Gbps SATA port support.

As you've surmised the ST3000DM001 drive can't saturate a 3Gbps port based on its sustained read figure (210MB/sec => ~ 1.7Gbps) so any benefit you would get would be limited to burst transfers out of the cache -- I would connect it to a 3Gbps port.


Spinning disk has a hard time getting up to 6Gbps speeds - In practice as of April 2012 only a few high-end 15K SAS drives can come close to 6Gbps performance (e.g. the IBM 44W2244 clocking in at 4.7Gbps), and the only drives that can saturate 6Gbps SAS or SATA connections are solid-state disks.

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6  
This is due to shady marketing practices used by spinning rust hard drive manufacturers, sata "6 Gbps" ratings are "burst" ratings, this only lasts for a few milliseconds, then it is up to the hard drive platters (rotational speed and platter density) to sustain any increased transfer rates due to the quality and design of the hard drive. They had to do something to continue to sell consumer grade hard drives based on performance increase over the last Sata spec that was adopted. In the end consumers are misled and uninformed. –  Moab Aug 28 '12 at 16:10
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@Moab All HD performance figures are a crock. In this case the drive has a 6Gbps controller, and is capable of 6Gbps transfers out of its (64MB) cache, so for the 0.1sec it takes to flush the cache you might see 6Gbps on the wire. Fortunately manufacturers are usually good about providing maximum sustained transfer rates so you can do the math yourself, but remember even those are a work of fiction: they're based on optimized sequential reads. –  voretaq7 Aug 28 '12 at 16:24
    
at voretag7, i was trying to be nice about it, thanks for saying what I wanted to say. –  Moab Aug 28 '12 at 20:00

There are some advantages to a faster bus, even if a single spinning drive can't sustain that bandwith:

  1. faster drives. Both higher-density magnetic drives, high-end SSDs and hopefully memristor-based drives can perform at high enough bandwidths as to make the faster bus a need.

  2. big caches. some manufacturers slap a flash device on the drive, to act as a transparent write-through cache, this can be much bigger than the usual RAM cache, so the drive can sustain faster speeds a little longer.

  3. drive arrays. Not too common with SATA connections, but there are some external eSATA enclosures, or maybe...

  4. ...not SATA but SAS. Since SAS and SATA share the same electrical and low-level specifications, improvements on one are quickly transferred to the other technology. Not only SAS drives are available on higher RPMs, but it's also very common to use SAS as a multi-device bus, which leads to the next...

  5. ...SATA multipliers/switches. Increasingly common, these devices allow you to use a big number of drives and external boxes on a small number of channels. It's almost as SAS!

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+1 -- If you're chaining drives in any form the higher bandwidth port (matched to lower-bandwidth drives) will help you maximize throughput without tying up more ports. –  voretaq7 Aug 29 '12 at 16:03

The difference between these would be minimal because a hard disk's transfer rate is lower than 3GB/s.

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