[Engine-devel] Issues with VirtIO-SCSI

[Ayal Baron]

----- Original Message -----
> Hi Daniel,
> 
> I asked this question because I have implemented a filter to show only
> compatible disk interfaces (in change #17964). The main purpose of this
> patch is to hide the IDE interface type when creating disks for PPC64 VMs
> (since IDE is not supported on this architecture). If it was decided that
> the VirtIO-SCSI interface type should be hidden from the user in case it was
> disabled, I would have to modify that patch a little bit.

That is not the case.  Point is to allow users to add a scsi controller to a VM that does not have any scsi disks. This is needed in case the user would later on like to hotplug scsi disks.  Without this, hotplug would fail since there is no scsi controller in the VM.
When the VM is down, you can always attach a scsi disk and if there is no scsi controller then engine will automatically add one.

> 
> Another issue is that in change #18622 the support for a PPC64-specific
> controller, the SPAPR VSCSI controller, was introduced. But the code was
> created based on the assumption that the VirtIO-SCSI controller was always
> present, and this isn't the case anymore. And another patch that I will work
> on really soon will add support to create disks that are connected to this
> interface.
> 
> So, I would like some feedback before changing these patches. Is a validation
> on the backend enough to block the user from using an inexistent controller?
> Should the frontend be changed as well? What would be a good approach to
> handle multiple SCSI controllers in a VM (were the presence of one of them
> is optional)?

If you have a need for a VM with more than 256 LUNs then I'd say that the easiest behaviour to understand would be to hide the existence of the controllers from the user altogether and just add support to automatically hotplug controllers on the fly when existing controllers are reaching their limit.


> 
> Thanks,
> Vitor
> 
> 
> 
> >-----Original Message-----
> >From: Daniel Erez [mailto:derez at redhat.com]
> >Sent: segunda-feira, 23 de setembro de 2013 17:06
> >To: Vitor de Lima
> >Cc: engine-devel at ovirt.org
> >Subject: Re: [Engine-devel] Issues with VirtIO-SCSI
> >
> >Hi Vitor,
> >
> >The new VirtIO-SCSI enabled checkbox is an indication whether to attach a
> >VirtIO-SCSI controller when running the VM.
> >It should be enabled automatically on cluster >= 3.3.
> >
> >When disabled, I think it's preferable not to add a new controller
> >automatically
> >when running the VM as it requires creating/attaching a new VmDevice -
> >which we refrain of on VmInfoBuilder flows (and since it might be confusing
> >to
> >the user...).
> >
> >As an alternative, I've planned to add a warning in the dialog or create a
> >canDo
> >message to prevent running the VM at all.
> >I'm not sure we should hide the option from disk interfaces list as it's
> >already
> >being filtered using VirtIoScsiEnabled ConfigurationValue (and using OsInfo
> >soon...).
> >
> >Let me know what you think and thanks a lot for the input!
> >
> >Daniel
> >
> >----- Original Message -----
> >> From: "Vitor de Lima" <vitor.lima at eldorado.org.br>
> >> To: engine-devel at ovirt.org
> >> Sent: Monday, September 23, 2013 10:42:39 PM
> >> Subject: [Engine-devel] Issues with VirtIO-SCSI
> >>
> >> Hi everyone,
> >>
> >> I have found some issues with this patch:
> >>
> >> http://gerrit.ovirt.org/#/c/18638/
> >>
> >> It allows the user to disable the VirtIO-SCSI disk interface during
> >> the VM creation. The problem is that the user still can add, attach
> >> and hotplug disks with the VirtIO-SCSI interface type, but when the
> >> user does so, libvirt automatically creates a LSI Logic SCSI
> >> controller and connects the new disk to it.
> >>
> >> How can this problem be solved? Should the VirtIO-SCSI interface type
> >> be hidden from the user in case it wasn't enabled, or should the
> >> engine enable the VirtIO-SCSI controller, hotplug it, then hotplug the
> >> disk into it transparently?
> >>
> >> Thanks,
> >> Vitor de Lima
> >>
> >> _______________________________________________
> >> Engine-devel mailing list
> >> Engine-devel at ovirt.org
> >> http://lists.ovirt.org/mailman/listinfo/engine-devel
> >>
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