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i'm using qemu-kvm(1.1.1) to run a Windows 2008 R2 Virtual Machine. The host machine is running CentOs 6.3. I'm exporting a USB 2.0 Hdd device to the VM using USB-redirection with spice channel. So far, everything is working fine, except that the speed is very slow. I'm getting 5MB/s max, against 25-30 MB/s when the hdd is mounted on hte host directly. Do you have any idea of what could cause such a limitation. Is there any tweak to increase the speed. Any help would be very much appreciated.


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This is a limitation with how the USB is redirected over the network. Its not just an issue with network performance but Qmenu/kvm implementation it self perhaps some thing they will improve on on later releases.

Try using Using USB pass-through instead of spice over the network. I think the spice is good when you are trying to mount USB from the thin client. But if you are plugging up the USB right into the server USB pass-through will give you the performance you need. Make sure that the USB is not mounted on the host system.

you can get the vendor id using /sbin/lsusb look for "ID :" of the desired USB device

Edit your vm config file.

    <hostdev mode='subsystem' type='usb'>
        <vendor id='0x0a5c'/>
        <product id='0x2110'/>
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