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Understand LAN data transfer speeds

Understand LAN data transfer speeds

I recently purchased a NAS (network attached storage) device from Synology, connected it to my network, and started transferring files. The first thing I noticed was the slow transfer speed of the network.

I was copying large video files and it was taking forever! I decided to check the transfer speed between my NAS and my PC to see the data transfer speed.

I downloaded a program called LAN Speed ​​Test, which got rave reviews and gave it a try. In fact, my download speed was less than 40MB / s! Note that this is megabytes per second, not megabits per second. I’m going to go into more detail about Mbps vs MBps and all that technical stuff.

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After doing some research, I found out what I was doing wrong and finally got a transfer speed of up to 85MB / s and super fast loading of 110MB / s. Technically, you can only reach this speed if you are using Gigabit Ethernet.

If you have 10 Gigabit Ethernet, you could theoretically get 10x faster upload and download speeds. I’ll also explain it in more detail below.

LAN data rate units

First, let’s clear the numbers. There is a standard 100 Mbps Ethernet network, which most people have at home. 100 Mbps is 100 megabits per second. This translates to 12.5 megabytes per second (Mbps or MB / s). It is much easier to convert to MB as it is something we all know rather than bits.

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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 at which you can transfer a file over your home network is 12.5 Mbps.

Furthermore, in the real world, it is impossible to obtain this theoretical maximum. It will probably end between 4 and 8 Mbps. If you get something really low, like 1 Mbps or less, there are reasons for that which I will mention below.

Keep in mind that even if your computer has a Gigabit Ethernet card, you will not get these higher transfer speeds unless all the devices on which the data is transmitted over the Gigabit medium.

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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 speed increases to 1000 Mbps or 125 Mbps (125 megabytes per second).

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

Finally, the latest devices can be upgraded with 10GB network cards. Of course, you will need a switch that can handle 10GB as well, but as you can see from the graph, the transfer speed is 10 times faster than most people currently use.

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If you’re working with a ton of video files that need to be transferred over the network, upgrading your hardware will dramatically improve your workflow. Fortunately, Cat5e cable can handle 10GB over shorter distances. If you need to install new wiring, it must be Cat 6a or Cat 7.

Transfer speed depends on what?

So, as we mentioned earlier, the network transfer speed depends on the type of Ethernet you have in your network, but it is not the only factor. Several other factors determine the final transfer speed between two devices.

Hard drive speed

A major limiting factor is the speed of the hard drive. If you have a 5400 RPM computer, your transfer speed will be much slower than if you have two SSDs in a RAID 0 configuration. How? ‘Or what? In fact it depends.

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

If you read online, you will find that even most hard drives (SATA 3.0Gb / s) reach a read speed of 75MB / s. This means that you won’t even be able to get past that without upgrading to more expensive configurations like RAID 0.1 or 5 with real hardware RAID controllers.

When upgrading to an SSD, things go faster. However, to get the results I showed you above (almost 110MB / s), you probably need a super fast NVMe SSD. These drives can read and write up to 3000MB / s, much more than Gigabit Ethernet.


Bus speed

Even if you have a fast hard drive, the data still needs to be transferred from the hard drive to your motherboard and then to the network card. The speed of the bus makes a big difference.

For example, if you are using an older PCI bus, the data transfer rate is only 133 MB / s. It may sound louder than the maximum for Gigabit Ethernet and it is, but the bus is shared throughout the system, so you never get that speed.

The latest version of PCI Express will give you a maximum of 985MB / s, which makes a big difference. This basically means that if you are trying to transfer files from a very old computer and even if you buy a Gigabit Ethernet card, don’t expect to get anywhere near the maximum transfer speed of 125MB / s.

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Network cables

Another aspect of all this is the wiring. If your cables are old or close to power sources, it can affect performance. Also, the length will make a difference if the cables are very long.

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

The main point from there is that the hard drive is a major limiting factor and is the most likely reason why you will only see results ranging from 30-80MB / s. To get really high numbers, you will need RAID 0 for traditional hard drives, NVMe for SSDs, or 10GB peripherals.

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Network devices

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

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

Second, you won’t get high speeds if you connect via WiFi from your PC or laptop. You must make sure that you are using the Ethernet port to get the fastest possible speed.

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File size

I’ve also noticed that transferring a ton of small files is slower than transferring fewer and larger files. For example, when transferring thousands of photos to multiple directories, you would get a transfer rate of around 20-60MB / s, while transferring large multi-GB video files would give you over 100MB / s +.


Hope this article gives you a better understanding of what affects network transfer speed on your LAN. It was never a problem that interested me long before, but after buying a 4K video camera, I was forced to buy a NAS to handle all that extra data.

Very slow transfer speeds allowed me to analyze my network and I learned a lot along the way. Even if you don’t care much about transfer speeds right now, there may be a time in the future when it suddenly makes a big difference.

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Let us know your thoughts in the comments. What kind of speed are you getting on your local network? Enjoy!