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I have a Ubuntu 11.10 x64 guest running under Hyper-V on Windows Server 2008 R2 SP1, configured according to these directions, including installation of the hyper-v modules. Network speed is fine (500 MB/s, measured with iperf), but disk access is laughable (3 MB/s, measured with dd).

What could possibly be causing this issue?

My other Ubuntu VMs have the same problem, my Windows VMs do not have this problem.

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thanks for fixing my spelling @Jacob :) I've been spelling it "uBuntu" for years, but google tells me I'm pretty much alone in that. I wonder where I picked that up? – Boinst Feb 24 '12 at 2:36
Out of curiosity, do you have the same issue with CentOS 6 after you install the integration tools? – Will Feb 27 '12 at 3:36
I have not tried CentOS. I've only tried Ubuntu and Windows 7. I do need to run Ubuntu ultimately because it's part of a continuous integration process that needs to pass its unit tests and build ubuntu binaries for shipping. If installing a CentOS VM would help for diagnostic purposes I can do that, but I can't imagine how it would. My current best option is to convert the server to an ESXi host. – Boinst Feb 28 '12 at 2:56
Are you using IDE or SCSI controllers for your virtual disks? – Bigbio2002 Feb 28 '12 at 4:11
@Bigbio2002, the default: IDE. I'll switch it and see if it makes a difference. – Boinst Feb 28 '12 at 4:37

I'm not sure if this has been fixed, but at one point you had to enable the Hyper-V modules in Ubuntu 10.04/2.6.x kernel (/etc/initramfs-tools/modules):





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Did that. Edited /etc/initramfs-tools/modules, did update-initramfs -u, rebooted, and confirmed modules were running with the command lsmod | grep hv_. Good suggestion though, that could be the cause for others with the same problem, thank you. – Boinst Feb 27 '12 at 2:38
@Boinst did it fix the problem in any way? – Nils Feb 28 '12 at 20:29
@Nils, I followed these steps before posting my question. I will update the OP to note this fact. – Boinst Feb 29 '12 at 0:12
up vote 0 down vote accepted

Unfortunately, Hyper-V is just not that great for virtualising linux. Use VMWare Converter to convert the server to an ESXi image, install ESXi on the server, then run the Windows machine as a VM. You can run the Ubuntu VMs as ESXi images with much better performance than you can get under Hyper-V.

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