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Slow Gigabit Network

Last response: in Networking
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September 27, 2012 8:38:58 PM

Hi,

I have just assembled a new Server with a high performance ASUS motherboard (6gb/s SATA connectors and USB 3 connections), i3 processor and 4 GB RAM. I have added 2TB and 3TB 7200 rpm drives with SATA 6gb/s connectors. When I checked the disk speed within linux I got over 180 mb/s but when I transfer files over network, I am getting about 30-40 mb/s.
What could really be the bottleneck.

Cheers,
D

More about : slow gigabit network

September 27, 2012 10:12:37 PM

I assume you have a Gigabit switch, Gigabit NICS on the other PCs, and CAT6 cables?

Remember, you can only transfer files as fast as the slowest link, and those links include the PC's hard drive.
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September 28, 2012 5:09:09 AM

Yes, all of the above assumptions are correct. The harddrives are 6gb/s SATA drives with 7200 rpm. I don't think it's the harddrive that are slow. What could it be really..
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September 28, 2012 9:18:44 AM

Cat5e also accepts Gigabit connections.
Remember to differentiate between MB and Mb. Your harddrive speed will be measured in MB/s and your network in Mb/s. This means that your hard drive is still working at 320Mb/s over the network, plus your Ethernet overheads, around 10%, you are probably hitting near enough, the correct speed. I would maybe look at the hard drive you are copying from. Is it the same spec, age, rpm? I've never known anyone to reach the full speed of a Gigabit LAN connection in 1 data transmission. If you had files being copied between multiple devices at the same time, you may get close.
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September 28, 2012 1:58:55 PM

The harddrives have nothing to do with the spped you are getting over the network... Phil is talking about the network switch, network adapters and cables linking them together. Do you have a Gigabit switch? do your PCs all have Gbit NICs, are the cables connecting them to the switch Cat5e or Cat6?
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September 28, 2012 2:12:47 PM

He must be, if he is getting 30 - 40 MB/s, then he is getting at 240 - 320 mb/s, so unless he has aggregated 4 fast ethernet ports into his computer, then he must be running on a Gb network.
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September 28, 2012 2:14:58 PM

Im going with Philfrisbe and ngrego, you should check your nic's.
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September 28, 2012 4:39:08 PM

All NICs are Gigabit. I am copying from Linux machine running samba, the motherboard is P8B75-V (http://www.asus.com/Motherboards/Intel_Socket_1155/P8B7...) which has a Gigabit LAN card. On the other hand, I am running MAC mini which also has a gigabit LAN. The harddrive is 3TB Seagate Baracudda. Below is the command I run to check the speed of harddrive on my linux box and the results are below:

# hdparm -tT /dev/sda1

/dev/sda1:
Timing cached reads: 7716 MB in 2.00 seconds = 3858.68 MB/sec
Timing buffered disk reads: 540 MB in 3.00 seconds = 179.89 MB/sec

On another note, I am running a Synology DS3612xs(http://www.synology.com/products/product.php?product_na...) and it gives me over 110 MB/s data transfer speeds.

Would be great to have the same speed on my home server too. I have a cat 6 connection.
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September 28, 2012 4:49:54 PM

As I was saying earlier, the speed of your hard drive is irrelevant as your network will never let you get that fast. A 1 Gigabit/second network can only ever transfer a maximum of 125 Megabytes/second of data, including all your overheads and everything else.
The bottleneck is the network, try allowing jumbo frames on switches, NICs and file server.
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September 28, 2012 4:50:15 PM

To add to the above, below is the output for network connection from the linux machine:

#ethtool eth0 | grep Speed
Speed: 1000Mb/s
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September 28, 2012 5:51:21 PM

Jumbo frames are switched on for both pcs and also the switch supports it (DIR-655). I want to hit atleast 100 MB/s which should surely be achievable on my network.
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September 28, 2012 9:43:03 PM

Toms hardware did an article over this very thing not too long ago. In fact it is the hard drives often that are the bottleneck of your gigabit network. The theoretical limit for a gigabit network, where all cable and NICs on both the server and client connection are all gigabit, is about 120 MB/s to 125 MB/s. In reality, due to additional network traffic such as ARP and possible signal attenuation over distances, you're looking at actually getting about 100 MB/s to 110 MB/s ideally.

This is still higher throughput than your normal desktop 7,200 SATA hard drive. Most mechanical hard drives, even SATA III drives, get an average throughput of about 80 MB/s. This then is where your bottleneck is going to be. If you can get your hard drive throughput greater than about 120 MB/s average then you have completely saturated the possible throughput of gigabit networks, so you need to look into either high-speed enterprise SAS drives or SSDs to get this kind of average throughput. And again, you'd have to have that kind of hard drive on both ends of the data transfer, both the server and client. The network will only operate during a transfer at the speed of the slowest component.

Still, looking at your recorded numbers they do seem a little low, at 30 MB/s. That's still pretty good though depending upon the network traffic, the number of computers on your network, the type of gigabit switch you are running, and any possible signal attenuation. Sometimes just having power cables running near your cables can nearly cut your network throughput in half.
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October 5, 2012 7:19:04 AM

Guys found a solution. I connect a Windows PC to the network and tried to copy and the network does over 120 MB/s as expected. The issue seems to be MAC mini even though it is set to Full Duplex 1000 baseT with 9000 MTU. I will now troubleshoot MAC mini instead of the network.
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