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  • If you're seeing <5Gbps on a 10Gbps link, that's because either the server or the client is not properly tuned for 10Gbps, or because of Smb/Cifs protocol overhead. Raw network performance of a 10Gbps link should be very close to 10Gbps if you've set it up right.
    – Darth Android
    Commented Sep 8, 2014 at 15:53
  • Re: protocol overhead... never said otherwise. On 1gbit smb/cifs allows up to 125MdB writes (thats 125 million, not 1024^3), and 119MdB Reads. Note that the above are in MB/GB speeds using 1024 as a base.
    – Astara
    Commented Sep 8, 2014 at 15:59
  • I'm confused by your "P.S." statement, as regardless of how the data is encoded on the wire, 10Gbps is 10Gbps. The link layer (1Gbps, 10Gbps, 40Gbps) operates at the given speed, and any overhead due to encoding on the Ethernet or IP level (for headers and such) will apply to all of them.
    – Darth Android
    Commented Sep 8, 2014 at 16:12
  • From the link above on 8b/10b it lists technologies that this applies to. One that is not 8b/10b encoded is Gigabit Ethernet twisted pair–based 1000Base-T Gigabit Ethernet, which seems to be the most common. They also mention the PCI-E bus for speeds below 8Gt/s -- so maybe when you get to 40&100 you are on a faster bus? That last is a guess, but I remember in the same article telling me about 10G using 8b/10b, that 1000BT didn't and thought it also said 40/100 didn't. But can't find that article. The link shows most common Gb not using that encoding.
    – Astara
    Commented Sep 8, 2014 at 16:22
  • 1
    Oh, I see the bad assumption I made. Twisted copper pair (1Gbps, 10Gbps, 40Gbps, +) does not use 8b/10b, but the fiber variants do. However, 10Gbps is still the effective speed ("These standards use 8b/10b encoding, which inflates the line rate by 25%") - so the physical fiber lines are carrying 12.5Gbps raw or 10Gbps effective. The math about PCIe 2.0 speeds at the top of my post does already include the overhead for 8b/10b encoding (hence the use of "effective bandwidth of 4Gbps per lane")
    – Darth Android
    Commented Sep 8, 2014 at 18:25