Network jams copying files Windows 2008 server, Proxmox

We have a Windows 2008 server primarily used for samba. It is not a domain controller.
It works 95% of the time, however, when reading/copying files from the server we experience network jams/lockups.

This usually happens when:
- using Acronis backup to copy a single large image file
- running batch files which copy large numbers of single files
- streaming videos (50-80MB) in size, causing lockups on the client.

The jams last between 10 and 90 seconds, during which little/no other network activity can occur.

The Windows 2008 R2 running inside a Proxmox virtualised environment V3.0-20/0428106c
We have followed the advice here, installing VirtIO network drivers and baloon driver.
http://pve.proxmox.com/wiki/Windows_2008_guest_best_practices

When the jams are in process, resource meters do NOT show any excessive CPU or network usage.

The server was setup similarly in a non-virtualised environment a few months ago worked fine.

Any ideas how to solve, or provide further diagnostic information.
Stuart LandrethAsked:
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Red-KingIT ManagerCommented:
I've come across a similar issue in the past with Windows 7 clients to Server 2008 R2.
The solution that I found to work was to disable the taskoffload and autotuninglevel features on the Windows 7 clients NIC.

netsh int ip set global taskoffload=disabled
netsh interface tcp set global autotuninglevel=disabled

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Stuart LandrethAuthor Commented:
Thanks for the suggestion though I don't think the issue lies with the client....

Some of our clients are windows xp
Also this happens when imaging new PCs using acronis backup which runs its own (linux-based) environment to do the restore operation.
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Red-KingIT ManagerCommented:
In that case, have you tried using Wireshark on the client PC to see what is happening on the NIC when the connection stalls?

This sounds like there might be something happening on the switch you're connecting to. It may be a broadcast storm or a faulty link that is causing the spanning tree table to be rebuilt.
Are there any routers or firewalls between the clients and the server? Any routing protocols being used?

As an aside, why did you settle on Proxmox compared to VMWare or HyperV? I'm just curious.

Rory
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Stuart LandrethAuthor Commented:
Hi Rory.

We settled on Proxmox as it is open source, and for the level of virtualisation we required (one server) not something we could justify spending money on.
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Stuart LandrethAuthor Commented:
One of our IT techs found the solution in then end - by changing the hard disk image type in Proxmox from QCOW to RAW the lockups were eliminated
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Stuart LandrethAuthor Commented:
Further to previous comments, this only reduced the frequency - it did not solve the problem.

We were unable to find a solution. In the end we just had to devirtualise the server whereby everything worked perfectly.
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Stuart LandrethAuthor Commented:
The problem was not solved. We had to change our infrastructure to avoid the problem occuring.
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