Networks Erratic gigabit lan speeds *SOLVED*

Hi guys.

I've had a Ubuntu server running on my network for quite some time now and the file transfer speeds always seemed a little "mediocre" for a gigabit lan. Last night, I was fooling around with some other stuff and I tried increasing the mtu on the server to 7200 (the highest value it's Netgear nic supports) and my main desktop machine to "jumbo" frames of ~9000.

Once both settings had "stuck", I downloaded a 700MB video file from the server to my desktop and was amazed by the speed. I got a sustained transfer rate of up to 50MB/s (which I'd imagine is the limit of the sustained write capability of my Samsung Spinpoint). Uploading files to the server was also very quick, though limited by the slightly slower WD drive (around 45MB/s).

The transfers were certainly a fair bit quicker than they used to be and for the first time it seemed like my network transfers were as quick as copying to a local drive. As a result, I set the mtu settings permanently.

However, I just went to move some files around again today (between the server and my main desktop) machine and the transfer rate has fallen quite dramatically in both directions. I'm getting around 10MB/s now and obviously, it's a noticable difference.

I've checked the mtu settings and they're all good and tried rebooting both machines but I can't get the speed close to what it was last night.

Any ideas?

 

space invaders?

Edit: Anybody else connecting to the server at the same time?

 

Nope, just me at the mo mate.

Can't get my head round it

EDIT: SOLVED!

Turns out the problem was with the onboard nic on my main rig. For some reason, it appears the new mtu settings sent the auto-negotiating feature a bit do-lally and it was picking 100mbps as it's operating speed, instead of 1000mbps. I went into the properties for the nic and changed the setting from auto-negotiate to 1000mbps and it's working great now!

Infact, my download speed (from the server) is even better than it was previously ~ 70MB/s, and my upload speed (to the server) is around 55MB/s. So all in all a win-win

 

Does this mean your router has to translate between MTUs (at least for outgoing packets) when you talk to "the cloud" (*cringe*)?

 

I guess that depends on the MTU between my router and "the cloud". And then between the next hop router and the router after that and ..... well.

The way I understand it, a packet on it's way through the internet will traverse many networks with potentially many of them having different MTUs. I thought that was the whole point of segmentation and reassembly? Or am I missing something?