Slow Hyper-V guest data transfer

[todarsey]

Well, I have taken and created a brand new VM. I installed the OS then installed SP3, then installed Hyper-V client services and then all other windows updates. The fastest that machine will do is about 20Mbps. So, I'm still at a loss of what the problem is.

[Mr Snrub]

Is the VHD file for the child partition on the same physical disk as the host is using for the destination?

That would be the same as doing a file copy within the same volume - there is only 1 disk read/write head so copying data will be around half as fast as it could be.

Physical clients on the network wouldn't incur this problem because they are accessing their local disks in parallel with the file server.

[todarsey]

Is the VHD file for the child partition on the same physical disk as the host is using for the destination?

That would be the same as doing a file copy within the same volume - there is only 1 disk read/write head so copying data will be around half as fast as it could be.

Physical clients on the network wouldn't incur this problem because they are accessing their local disks in parallel with the file server.

No, all VMs are on a different hd. The VMs are on local drive E: and they are looking at drive F: to do the speed test. (I think this is answering the question)

[Mr Snrub]

Strange... I just did a clean install of XP SP2, installed the Integration Services, applied SP3 and then did a copy of the SP3 installer (316MB) from the VM to a different disk on the host machine, which took ~19 seconds with an Explorer drag & drop operation and 13.4 seconds from the command line.

For comparison, the same file copied to the host volume where the VM's VHD is held took ~21 seconds in Explorer and 14.4 seconds from the command line.

WindowsXP-KB936929-SP3-x86-ENU.exe is 331,805,736 bytes, which would put the approximate average throughputs at:

Explorer, different volume: 139.7 Mbps

Command line, different volume: 198.1 Mbps

Explorer, same volume: 126.4 Mbps

Command line, same volume: 184.3 Mbps

The Hyper-V host is Windows Server 2008 R2, not Windows Server 2008 SP2, however - I don't have a W2K8 Hyper-V host to do a similar test unfortunately.

The host is also standalone with no other roles except File & Print Server.

Copying the same file to a VM on the same host, but whose VHD file was on a different volume, took ~8.5 seconds through both Explorer and from the command line.

I know that Windows Server 2008 R2 supports VDI with Hyper-V and the Remote Desktop Services roles, but I don't know of any serious changes to Hyper-V to make non-Server versions of Windows run better then previously... has anyone else got XP running under Hyper-V on Windows Server 2008 and can comment on network throughput from guest to host or guest to guest?

[jcarle]

I suggest running iperf between your VM and the host to determine if it's a network issue or a disk issue.

The iperf binary can be downloaded from here : http://www.noc.ucf.edu/Tools/Iperf/default.htm

On one end, start iperf in server mode with the command line : iperf.exe -s

On the other end, start iperf in client mode with the command line : iperf.exe -c <clientip>

[Mr Snrub]

What if you use a Private network instead of an External one, do you get the same kind of throughput between the child and parent partitions?

Can you set up a Private virtual network and connect the XP guest to it instead of the External network, put static IPs on the host and the client and then see if the throughput is the same?

[todarsey]

What if you use a Private network instead of an External one, do you get the same kind of throughput between the child and parent partitions?

Can you set up a Private virtual network and connect the XP guest to it instead of the External network, put static IPs on the host and the client and then see if the throughput is the same?

On an internal network I get 100Mbps on the XP machines

[jcarle]

Did you test with iperf?

[todarsey]

Did you test with iperf?

I have just now run it. On the XP VM I get 28.8Mbps, on a physical machine I get 192Mbps.

[Mr Snrub]

Okay, so we know it's something specific to the virtual network bound to the physical NIC - the same partitions communicating using the same disks over a private virtual network run at a reasonable speed, yes?

At this point I'd be looking at what options exist for updating the drivers in the root partition for the NIC.

I would move all child partitions onto a private or internal network temporarily, then remove the external virtual network, giving it back to the host.

Then I'd check for different drivers for the NIC and install them, and ensure in the properties of the NIC that all "advanced" features are off (jumbo frames, offloading, etc.).

Then I would recreate the external virtual network and move the child partitions back onto it.

(You would have to move the child partitions off the virtual network first, as Hyper-V Manager will not let you delete a virtual network which has partitions on it.)

Does the host have a dedicated NIC, and you are using a separate NIC for the external virtual network?

Or is it just 1 NIC used by the host and VMs?

[todarsey]

I have also run iperf on my WHS VM and got 297Mbps. Would this still be a problem with the physical NIC? This NIC is an Integrated Realtek RTL8168/8111 PCI-E.

[jcarle]

My suspicion is that the virtual network adapter driver is having issues in your VM. Make sure your host has all windows updates, uninstall and reinstall the integration components within the VM that's affected and try deleting the NIC completely from device manager (inside the affected VM) and re-installing it.

Also, you may want to consider upgrading your network card to an Intel based one for better performance. (Even if this may not be your issue.)

Edited August 10, 2009 by jcarle

[fizban2]

i would suggest deleting the virtual network and recreating it, i have flaky netowork issues before and deleting the the virtual NIC and recreating it as a last effort has helped.

[todarsey]

i would suggest deleting the virtual network and recreating it, i have flaky netowork issues before and deleting the the virtual NIC and recreating it as a last effort has helped.

Just did this, didn't work.

[jcarle]

i would suggest deleting the virtual network and recreating it, i have flaky netowork issues before and deleting the the virtual NIC and recreating it as a last effort has helped.

It's important to note that deleting the "network" may not yield any significant corrections to the problem. Deleting the network card within the VMs may yield better success. There's also the possibility of poor drivers for the host network card that should be looked at.