[libvirt-users] virtual drive performance

Dan srwx4096 at gmail.com
Wed Jun 21 18:46:37 UTC 2017


On Tue, Jun 20, 2017 at 04:24:32PM +0200, Gianluca Cecchi wrote:
> On Tue, Jun 20, 2017 at 3:38 PM, Dominik Psenner <dpsenner at gmail.com> wrote:
> 
> >
> > to the following:
> >
> > <disk type='file' device='disk'>
> >   <driver name='qemu' type='qcow2' cache='none'/>
> >   <source file='/var/data/virtuals/machines/windows-server-2016-
> > x64/image.qcow2'/>
> >   <backingStore/>
> >   <target dev='hda' bus='scsi'/>
> >   <address type='drive' controller='0' bus='0' target='0' unit='0'/>
> > </disk>
> >
> > Do you see any gotchas in this configuration that could prevent the
> > virtualized guest to power on and boot up?
> >
> >
> When I configure like this, from a linux guest point of view I get this
> Symbios Logic SCSI Controller:
> 00:08.0 SCSI storage controller: LSI Logic / Symbios Logic 53c895a
> 
> But htis is true only if you add the SCSI controller too, not only the disk
> definition.
> In my case
> 
>     <controller type='scsi' index='0'>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x08'
> function='0x0'/>
>     </controller>
> 
> Note the slot='0x08' that is reflected into the first field of lspci inside
> my linux guest.
> So between your controllers you have to add the SCSI one
> 
> In my case (Fedora 25 with virt-manager-1.4.1-2.fc25.noarch,
> qemu-kvm-2.7.1-6.fc25.x86_64, libvirt-2.2.1-2.fc25.x86_64) with "Disk bus"
> set as SCSI in virt-manager, the xml defintiion for the guest is
> automatically updated with the controller if not existent yet.
> And the disk definition sections is like this:
> 
>     <disk type='file' device='disk'>
>       <driver name='qemu' type='qcow2'/>
>       <source file='/var/lib/libvirt/images/slaxsmall.qcow2'/>
>       <target dev='sda' bus='scsi'/>
>       <boot order='1'/>
>       <address type='drive' controller='0' bus='0' target='0' unit='0'/>
>     </disk>
> 
> So I think you should set dev='sda' and not 'hda' in your xml for it
> 
I am actually very curious to know if that would make a difference. I
don't have a such windows vm images ready to test at present.

Dan
> I don't kknow if w2016 contains the symbios logic drivers already
> installed, so that a "simple" reboot could imply an automatic
> reconfiguration of the guest....
> Note also that in Windows when the hw configuration is considered heavily
> changed, you could be asked to register again (I don't think that the IDE
> --> SCSI should imply it...)
> 
> Gianluca

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