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Network Switches and Data Transfer Speeds

Posted by Andrew at 5:17 PM on March 27, 2011

I recently upgraded my home network from 100 Mb/s to 1 Gb/s by replacing the switches. The main house switch is an unmanaged 1U rack-mounted switch, with a second desktop switch. Out of pure interest, I took the opportunity to do a little bit of speed testing to see how much of a difference upgrading the switches made in terms of actual data transfer speeds.

A few basics to avoid confusionĀ  – b/s is bits per second and B/s is bytes per second. All of the reported figures will be in MB, so converting b/s to B/s:
Fast Ethernet = 100 Mb/s = 12.5 MB/s
Gigabit Ethernet = 1 Gb/s = 125 MB/s

100 Mb/s and 1 Gb/s refer to the speed of the underlying technology but data transfers at these rates are never achieved because of protocol overheads and such. As a baseline, if I write a large file (8 GB) to my PC’s local disk, I get a data transfer of between 50-55 MB/s.

On my network, I have two Buffalo Linkstation NAS devices, one with a Fast Ethernet interface and one with a Gigabit Ethernet interface. 2 GB’s worth of data would be written to each of these devices with different Ethernet switches in place to see what actual data transfer speeds would be achieved. The following Linux command was used five times in each situation and the result averaged.

time dd if=/dev/zero of=testfile bs=16k count=16384
Switch Model Data Rate to Fast NAS Data Rate to Gigabit NAS
1U Rack
Dynamode SW240010-R(Fast) 6.2 MB/s 8.6 MB/s
TP-Link TL-SG1016 (Gigabit) 6.4 Mb/s 21.4 MB/s
Desktop
D-Link DES-1008D (Fast) 6.2 MB/s 8.6 MB/s
Netgear GS605 (Gigabit) 6.5 MB/s 21.1 MB/s

I also carried out two further tests:

  1. With Gigabit Ethernet only, I wrote to both NAS devices at the same time. The data transfer speeds were unaffected.
  2. I connected the two Gigabit Ethernet switches in series and wrote to the NAS. Transfer speeds were reduced by 1 MB/s on the Gigabit NAS to 20 MB/s. The change on the Fast Ethernet NAS was minimal.

There are several things that can be deduced from the information shown in the table above and the other tests.

  1. Actual data transfer rates are considerably less than the theoretical maximums.
  2. There’s no performance difference between rack-mounted and desktop switches.
  3. The write speed of the NAS can be a limiting factor.
  4. Gigabit Ethernet switches give large improvements with Gigabit Ethernet devices.
  5. Gigabit Ethernet switches give small improvements even with Fast Ethernet devices.
  6. Keep the number of switches in the network path to a minimum.

 

One Comment

  1. From Mauricio Catao Cruz Santos at 5:07 am on March 28, 2011

    I used to have the same problem… The problem was HardDisk Performance. Then I bought a Intel SSD, to speed up my system. I have installed the ssd 80gb as my First disk, and made it my Windows Boot Disk. Then I copied a 9GB file from my desktop folder to my home server(Linux RAID), the transfer rate reached 90 MBytes/s. Before it used to be arround 11 MBytes/s.

    Recently I made a home server to a friend of mine using 4 disks of 1,5TB each (Software RAID-5), resulting in 4,5TB of storage only for data. The System boots from a 2x500GB (RAID-1). The result was a cheap server with good security for all his data and excellent read performance.

    Take a look at this report below.

    http://www.tomshardware.co.uk/gigabit-ethernet-bandwidth,review-31611.html

    Good Lucky.