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Re: [vfio-users] Looking for performance tips, qemu machine type and pci/pcie-root questionning?




On Apr 15, 2016 9:01 AM, "thibaut noah" <thibaut noah gmail com> wrote:
> Speaking of drives, it seems from what i read that it is possible for qemu/kvm to read a native (non virtualize) install of windows from a passthrough drive.
> If so is there something special to do? Might go to the hassle of reinstalling my all windows system by i prefer to be sure before touching anything (though i might just backup the image, boot my vm from it and clone windows, much easier than reinstalling).
There is a problem, that i've promised to git bisect, but trashed my fedora instead.
The thing is, you give the whole drive (or just the necessary partitions) to the vm, and you can either boot the OS inside a VM, or run it bare-metal.
There are some culprits, for example:
If using UEFI, in order to properly mirror the install, you have to copy the efivars. Windows relies on them to activate itself.
If using not virtio-scsi, you don't send the scsi commands. The most noteworthy are SMART and TRIM.
And the final one, since some version of OVMF, GPT formatted drive gets checked for valid MBR and it fails to boot.
But the performance is closest i could get to native, my HDD gets around 150-180MBps, just as it does baremetal.
Not sure about IOPS though.
This kind of setup is useful for AB testing.


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