Understanding LAN Network Data Transfer Speeds

I recently bought a NAS (network-attached storage) device from Synology, connected it to my network, and started transferring files. The first thing I noticed is how slow the data transfer rate over the network is.

I copied several large video files and it took forever! I decided to check the baud rate between NAS and PC to see the baud rate.

I downloaded a program called LAN Speed ??Test, which got some great reviews, and tried it. Of course, my download speed was less than 40MB / s! Note that these are megabytes per second, not megabytes per second. I’ll go into more detail about Mbps and Mbps and all that technical stuff.

After doing a little research, I figured out what I was doing wrong and ended up with up to super fast download speeds of 85MB / s and 110MB / s downloads! Technically, you can only get this kind of speed when using Gigabit Ethernet.

If you have 10 Gigabit Ethernet, you can theoretically get 10 times faster upload and download speeds. I’ll talk about this in more detail below.

LAN data rate units

First, let’s get the numbers clear. There is a standard 100 Mbps Ethernet that most people have at home. 100 Mbps is 100 megabits per second. This translates to 12.5 megabytes per second (MB / s or MB / s). Converting to megabytes is much easier as this is something we are all familiar with and not bits.

This means that if you don’t have a gigabit router or switch and a gigabit network card in your computers or NAS, the maximum speed you can transfer a file over your home network is 12.5 Mbps.

Moreover, in the real world, it is impossible to obtain the theoretical maximum. You will probably get anywhere from 4 to 8 Mbps. If you’re getting something really low, like 1 Mbps or less, there are reasons for that, which I’ll cover below.

Note that even if you have a Gigabit Ethernet card installed on your computer, you will not get this faster transfer rate if all the devices to which the data is transferred do not support Gigabit speed.

If you have a gigabit Ethernet card in your computer, your router or switch is gigabit, and the receiving device also has a gigabit Ethernet card, your maximum transfer rate will increase to 1000 or 125 Mbps (125 megabytes per second).

Again, you won’t get this theoretical speed, but you should get between 70 and 115 Mbps depending on the type of files being transferred and your network settings.

Finally, the latest devices can be upgraded with 10GBe network cards. You will of course need a switch that can handle 10GBe as well, but as you can see from the diagram, the transfer rate is 10 times faster than most people are now.

If you work with tons of video files that need to be streamed over the network, upgrading your hardware will greatly improve your workflow. Fortunately, Cat5e cable can handle 10GBe over shorter distances. If you need to install new cables, it must be Cat 6a or Cat 7.

The conversion speed depends on what?

So, as we mentioned above, the network transfer speed depends on the type of Ethernet on your network, but this is not the only factor. There are several other factors that determine the final data transfer rate between two devices.

Hard disk speed

Hard drive speed

One of the major limiting factors is hard drive speed. If you have a 5400 RPM computer, the transfer rate will be much slower than if you had two SSDs in a RAID 0 configuration! How so? Well, it depends on the circumstances.

On my network, even with Gigabit Ethernet, I only get 40 to 50 MB / s when using a traditional hard drive.

If you read online, you will find that even most hard drives (SATA 3.0 GB / s) have a maximum read speed of 75 MB / s. This means that you cannot even avoid it unless you upgrade to more expensive configurations like RAID 0.1 or 5 with real hardware RAID controllers.

Things get faster when you upgrade to an SSD. However, to get the results I showed you above (around 110MB / s), you will most likely need a super-fast NVMe SSD. These drives can read and write at speeds up to 3000MB / s, well above Gigabit Ethernet.

Bus speed

Bus speed

Even if you have a fast hard drive, you still have to transfer data from the hard drive to the motherboard and then to the network card. Bus speed matters a lot.

For example, if you are using an older PCI bus, the transfer rate is only 133 MB / s. This may seem like higher than the maximum for Gigabit Ethernet, and it is, but the bus is common to the entire system, so you never get that kind of speed.

The latest PCI Express has a maximum speed of 985 MB / s, so this makes a huge difference. This basically means that if you are trying to transfer files from a really old computer, and even if you buy a gigabit Ethernet card, don’t expect to get close to a maximum transfer rate of 125MB / s.

Network cables

Network cables

Another aspect of all this is cabling. If you have old cables or are near power supplies, performance may be affected. Also, length will matter if the cables are very long.

Overall, however, it won’t make a big difference, so don’t go away and start replacing all of your cables. Basically you want to make sure you have CAT 5e or CAT 6a / 7 cables.

The main takeaway from this is that the hard drive is the main limiting factor and the most likely reason you will only see a range of results between 30 and 80 MB / s. To get really big numbers, you’ll need RAID 0 for traditional hard drives, NVMe for SSDs, or 10GBe devices.

Network Devices

Network devices

Finally, you should try to keep your two machines (NAS and PC) connected to the same switch or router. I connect my computer and NAS to the same switch and then I connect the switch to a wireless router.

Most routers are also switches, and technically you should get the same speeds as a dedicated switch. However, in my experience, a dedicated switch from Netgear or Cisco always performs better than a wireless router with built-in ports.

Secondly, you won’t get high speeds if you connect via Wi-Fi from your PC or laptop. You must make sure to use the Ethernet port to get the fastest speed possible.

File size

File size

I also noticed that transferring a ton of small files is slower than transferring fewer larger files. For example, if transferring thousands of photos to a group of directories, I would get transfer rates between 20 and 60 MB / s, whereas transferring large movie files of several GB would give over 100 MB / s +.

Conclusion

Hopefully this post will help you better understand what affects the data transfer rate on your local network. I never really worried about it before, but after I got a 4K camcorder, I had to buy a NAS to manage all that extra data.

The very low data rate made me analyze my network and I learned a lot in the process. Even if you don’t really care about your data rate right now, there may be a time in the future when it suddenly changes significantly.

Let us know your thoughts in the comments. What is your local network speed? Enjoy!

–