Problems with UDP-Connections

[Metrax]

Hi,

i want to use some UDP protocols like TFTP or NFS on a virtual machine.

The problem is, that I'm only getting ~300kbit/s on transferring a 100MB file.

With TCP protocols like HTTP or FTP the files can be received with full 100Mbit/s (switch port limitation).

When I'm transferring the files to a physical machine, I don't experience a speed problem, so I think that this is not a problem of the source server.

I've attached an image to this post, where you can see both connections.

The first peak is the connection via HTTP, the second peak is the connection over TFTP. Both files are 100MB.

Is there a solution for this problem?

Thank you very much.

Robert

[J1mbo]

TFTP operates in lock-step (there is no windowing) so any latency will seriously affect the throughput. Could you provide some general info about your setup - phyiscal cores, and vm vcpus in particular.

Please award points to any useful answer.

[Metrax]

Hi J1mbo,

Thank you for your reply.

Here is the information you have requested:

Hostsystem:

CPU: Intel Core i7 920 4*2,66 GHz

Cores: 8 logical (HT) , 4 physical

Motherboard: Asus P6T SE

RAM: 6x2 GB DDR3 Kingston 1333MHz

HDD: 2x1000GB Samsung S-ATA2

NIC1: Intel PRO/1000 PT Dual Port Server Adapter (100Mbit/s FD, Auto Negation, vSwitch0, Management Network)

NIC2: Intel PRO/1000 PT Dual Port Server Adapter (10Mbit/s FD, manually set, vSwitch1)

Virtual machine 1:

Guest: Debian GNU/Linux 5 (64bit)

VM-Version: 7

CPU: 2 vCPU

RAM: 8192 MB

RAM-Overhead: 197.44 MB

VMware Tools: not installed

Datastore: datastore1

Network: VM Network 100Mbit/s

Virtual machine 2:

Guest: other 2.6x Linux (64bit) (Cent OS 5.3 installed)

VM-Version: 7

CPU: 1 vCPU

RAM: 2048 MB

RAM-Overhead: 233.66 MB

VMware Tools: not installed

Datastore: datastore1

Network: VM Network 100Mbit/s

I've tested this problem with both virtual machines and both are having the same problem.

I hope that these facts are helpful to identify the problem.

Thank you very much!

Robert

[dburgess]

Are you seeing much packet loss?

We have seen different distro's drop significantly more UDP packets than others.

Have you tried the vmxnet driver - not sure if you would need tools or not.. but that may help..

Lastly I think we can tweek the Receive Buffer size on the vSwitch - I can't find the reference at the moment but that may assist.

dB

[Metrax]

Hi dB,

Thank you for your reply.

QUOTE: Are you seeing much packet loss?

QUOTE: We have seen different distro's drop significantly more UDP packets than others.

I didn't found a hint for such a high packet lost.

QUOTE: Have you tried the vmxnet driver - not sure if you would need tools or not.. but that may help.

I have tried this now, but it doesn't differs.

QUOTE: Lastly I think we can tweek the Receive Buffer size on the vSwitch - I can't find the reference at the moment but that may assist.

Where can i change this setting?

Thank you very much.

Robert

[dburgess]

This may also be useful:

http://blogs.vmware.com/networking/2009/04/considerations-for-maximum-network-performance.html

Im still looking for the rx ring buffer document - I think it is a setting on the vSwitch

dB