Slow network performance between VM's

[woutwoot]

Simple example, I have qemu guest running ubuntu 17.04 with samba file share server.
If I copy large files to it from my Windows 10 PC over the network, the speed tops out at around 120MB/s which is normal for my gbit network. However, when I mount the share on the proxmox host, or on another container, network speed seems to top out at around 40MB/s.
Does anyone have any clue why this is copying slower? I've also tried scp and rsync. To me this makes no sense as it should be as fast as the disk can write.
(the bottleneck is not disk read, I've tried with SSD and see the same issue, the CPU should also be more than fast enough and is not maxing out anywhere, the VM's all have 2Gb or more RAM)

Windows to guest and host to guest image:

 

[Alwin]

For network speeds, use iperf, as here you are testing a protocol, that is implemented differently on the various OS. I guess, the different servers use different SMB protocol versions and that's where the difference in transfer shows.

 

[woutwoot]

For network speeds, use iperf, as here you are testing a protocol, that is implemented differently on the various OS. I guess, the different servers use different SMB protocol versions and that's where the difference in transfer shows.

Thank you for that suggestion. I've used iperf to check the speeds, and they all seem more than fine (more than 2gbit/s). (I've tested host to guest and guest to host)
This would mean that the cause could be samba, but copying using rsync has the same low speed, so samba can be ruled out. Do you have any other tips I can use to diagnose the problem?

 

[Alwin]

This would mean that the cause could be samba, but copying using rsync has the same low speed, so samba can be ruled out.

rsync and scp from Windows? How are writes done and is there some caching in between.

I guess, the different servers use different SMB protocol versions and that's where the difference in transfer shows.

Check the protocol versions, of your samba clients and settings.

 

[raubo]

Copying large files from one KVM VM to another (all linux vms) makes immediately every other VM freeze. There should be a proper multitasking but obviously the copy process eats all resources. As soon as the copy is completed, everything goes on like before.
Is that normal with Proxmox or does it sound to you like a misconfiguration?
I used Univention KVM before and had never such an effect.

Best, Ralph

 

[Alwin]

@woutwoot and @raubo, check your storage throughput/latency and VM configuration (eg. cache settings). The data has to be written to the same storage, if you are not coping over network.

 

[raubo]

Please be more precise. What should the correct values be? Which cache settings?