Network throughput limited by MB hardware?

[acockburn]

Hi,

I recently upgraded my Internet to Cablevision Ultra - quoted at 101Mb/s download speeds, and I have had variable success in actually reaching this on a couple of my machines.

The problem is not with Cablevision, as I have frequently met and exceeded this download speed with other machines, I have seen up to 120Mb/s on speedtest.net.

- I have eliminated any infrastructure as a problem by swapping out switches, and have verified that the same physical cable from one of the problem machines on a different machine (my Macbook Pro) hits the expected speed
- I have a server class machine running ESXi, and even one of my Windows 7 VMs is capable of hitting 100+ with the onboard LAN adapter
- In all cases the NICs have auto negotiated to 1Gb/s (I also tried forcing 1Gb full duplex)
- I am testing with fairly fresh Windows 7 Installs

In focusing on one of the problem machines, using the onboard LAN adapter, I have tried 3 different mother boards, and reinstalled windows, and seen the maxed out speed increase from about 70Mb/s up to around 90Mb/s. Another machine that I have with an identical MB has around the same performance - the MB is an ASRock Z77 extreme6, previous MBs were 2 flavors of MSI boards. I also tried an intel PCIe NIC for comparison, and if anything it was slightly slower than the onboard NIC.

At this point I am suspecting some limitation in the hardware although it seems that the various bus speeds should be more than fast enough to handle this amount of data. The VM server hardware is about 4 years old and handles the bandwidth comfortably. I wouldn't ever expect to see 1Gb/s out of a 1GB NIC, but these speeds seem closer to 100Mb/s performance.

Can anyone shed any light on this? I am prepared to buy new hardware if necessary for at least one of my machines to figure out what the limitation is.

Thanks in advance,

Andrew

[edited to fix MB/s vs Mb/s]

 

[choucove]

Part of the issue you are having here is confusing MBps (MegaBytes per second) with what your network connection is probably quoted at Mbps (Megabits per second.) One byte contains eight bits, so a MBps is eight times the speed of a Mbps link. It might help in clarifying then if you have a 100 Mbps or 100 MBps connection.

When using a gigabit network infrastructure base, the realistic maximum throughput you are going to get is around 110 MB/s. Most standard 7,200 RPM hard drives also have an average throughput of around 100 MB/s. This means that transferring data from one computer system to another computer system is most likely bottelenecked first by the hard drive transfer throughput before it is bottlenecked by the network throughput, but it's going to be close.

If you are doing testing with transfer speeds, then it might be that your hard drive is your limiting factor. I have a (very small) test lab at my office that we have to use SSDs to eliminate the hard drive throughput bottleneck to test network speed transfer throughputs.

 

[acockburn]

Thanks for the response - sorry about that, I do know better - all figures I quote are in Megabits per second (Mbps). The link is rated at 101Mb/s, and I am seeing speeds of up to 90Mb/s on the problem machines, as high as 120Mb/s on other machines.

All the testing I have been doing has been using speedtest.net - I imagine that it doesn't actually write to disk, and given my clarification even if it did, I don't expect that disc throughput would be the limiting factor (I have SSDs on both of the problem machines). It's a good point though and I think I will try some machine to machine transfers for an additional data point.

 

[choucove]

With that information then, no it wouldn't seem your hard drives are in any way affecting the speed, as you are testing a direct internet connection speed normally done to RAM anyways. It's harder to say what could be causing the specific discrepancies you are having them in speed from one computer to another in your network, but my guess would have to be just the type of NIC or drivers. If nothing else, check and see if you can download the latest drivers from your NIC manufacturer directly and see if that makes any difference.

 

[acockburn]

OK, thanks for the suggestions!