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I very often hear SAS hard drives referred to as "6Gb/S".

However, when looking at actual specifications, the top benchmarks are in the 100s of MB/s.

Right here, the spec for the Seagate Cheetah states Interface: 6-Gb/s SAS.

What is the difference here?

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    6Gbit/s is the interface speed (maximum speed of the SAS interface). The actual drive data transfer speed is in the 100s of Mbyte/s range.
    – Dan
    Commented Apr 18, 2015 at 18:28
  • Ah. Interesting. So it's funny that drive specifications don't usually give an actual benchmark, just the RPM. Does that sound accurate?
    – dthree
    Commented Apr 18, 2015 at 19:32
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    It is a marketing gimmick to confuse the layman. If you want to know the real data rates of a drive, run it thru HD Tune. And focus also on the access time which is more important for the OS than the R/W speeds.
    – whs
    Commented Apr 18, 2015 at 21:01
  • Ah. Tricky. So, is it accurate to say SSDs run between 400/500Mbps, meaning one purchased for $80.00 @ Walmart is literally 4x faster than your best SAS HDDs?
    – dthree
    Commented Apr 18, 2015 at 21:09
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    First, consumer ssd will usually run at 200-and-some MB/s. Second, that is the linear access speed, which is only half the story. The real ssd deal is in the random acces, where it's 10-30x faster than a hdd. The only reason not to go ssd is the price (if your server only supports SAS and not SATA, a SAS ssd is way more expensive)
    – Dan
    Commented Apr 20, 2015 at 6:16

2 Answers 2

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6Gbit/s is the SAS interface speed, and not the actual harddrive speed (which is in the 100s of MBytes/s range, and that only if you are measuring the sequential transfer speed)

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You are misreading the form of measurement. GB/s is gigabyte per second. Gb/s is gigabit per second.

There are 8 bits in a byte.

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    True. However even with this, 6 Gb/s would be ~750MB/s, which is about 5x faster than the benchmark on this drive (?).
    – dthree
    Commented Apr 18, 2015 at 17:43

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