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Network Tests: Are We Getting Gigabit Performance?

Gigabit Ethernet: Dude, Where's My Bandwidth?

Let’s proceed with our first test, where we send a file from the client’s C: drive to the server’s C: drive:

We’re seeing something that mirrors our expectations. The gigabit network, which is capable of a theoretical 125 MB/s transfer, is sending out data from the client’s C: drive as fast as it can, probably somewhere in the neighborhood of 65 MB/s. However, as we demonstrated previously, the server’s C: drive can only write as fast as about 40 MB/s.

Now let's copy a file from the speedy server RAID array to the client computer’s C: drive:

Once again, this is just like we called it. We know from our tests that the client computer’s C: drive can write this file at about 70 MB/s under ideal conditions, while the gigabit network is delivering performance very close to this speed.

Unfortunately, none of these numbers have come close to gigabit's theoretical maximum throughput of 125 MB/s. Is there a way we can test the network’s maximum speed? Of course there is, but not in a real-world situation. What we’re going to have to do is make a direct memory-to-memory transfer over the network so that we bypass any hard drive-bandwidth limitations.

To do this, we’re going to make a 1 GB RAM drive on both the client and server PCs, and then transfer a 1 GB file between these RAM drives over the network. Since even the slowest DDR2 RAM should be able to handle over 3,000 MB/s of data, the only limiting factor should be how fast our network can run:

Lovely! We’re seeing a 111.4 MB/s maximum speed over our gigabit network, which is very close to a gigabit network’s theoretical 125 MB/s. This is a great result and is nothing to complain about, as real-world bandwidth will likely never hit an ideal maximum speed.

So now we've proven it conclusively: hard drives are the lowest common denominator when it comes to file transfers over a gigabit network, limiting a network's data transfer rates to that of the slowest hard drive. With this big question answered, we wanted to do a few network-cabling tests, just to satisfy our curiosity. Is network cabling a factor that might keep us from network speeds closer to the theoretical limit?

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