Re: [Xen-users] Status of PVSCSI

[Jon Schewe <jschewe@xxxxxxx>]

On 8/11/16 12:07 PM, Austin S. Hemmelgarn wrote:
> On 2016-08-11 11:47, Jon Schewe wrote:
>> On 8/5/16 10:38 AM, Jon Schewe wrote:
>>> On 8/5/16 10:27 AM, Simon Hobson wrote:
>>>> Jon Schewe <jschewe@xxxxxxx> wrote:
>>>>
>>>>> I'm looking to move my backups into a VM and PVSCSI seems like the
>>>>> right way to get the tape library and drive visible to the VM.
>>>>> ...
>>>>> So what front end can I use pvscsi with?
>>>> Can you use PCI passthrough of the SCSI controller ?
>>>>
>>> I have considered that, however I have a couple of issues with it:
>>> 1) When I tested it, after shutting down the domU the dom0 couldn't
>>> attach to the SCSI controller again until I rebooted. Perhaps that was
>>> because I shutdown the domU before calling pci-detach.
>>>
>>> 2) I see that I need to detach the pci devices before save and restore.
>>> That will make things hard when rebooting the dom0 for updates. I
>>> usually just run "service xendomains stop" and then run the updates and
>>> reboot. This suspends the domUs and everything is fine on startup. If
>>> this process will automatically handle the detach and attach calls,
>>> then
>>> I may be able to use it.
>>
>> Does anyone know if pci devices need to be explicitly detached before
>> shutdown or if xen will do the right thing on shutdown of the VM?
> In my experience, it depends on the device.  Some devices work fine
> (mostly really simple dumb devices, such as some really cheap GbE
> NIC's), but many need hardware re-initialization before they will work
> (and some like certain GPU's actually need a full power cycle before
> they work reliably).  For many of those that need hardware
> re-initialization,, you can unload and reload the driver in Domain-0
> to reinitialize the hardware, but only after you've detached the
> device from the VM and removed the reservations.
>>
>> Also if I call "/etc/init.d/xendomains stop" and the VMs are saved, will
>> that do the right thing or will I need to manually detach pci devices
>> that are passed through?
> You would have to detach the devices if you want to use them elsewhere
> before restoring the VM.  Think along the same lines as accessing the
> VM's disk image while it's stopped, the OS won't be expecting the
> change, and it may lead to data loss or other odd behavior.  Saving a
> VM is essentially the same in this case as putting a laptop to sleep,
> so you really should avoid doing anything with any hardware for the VM
> (real or emulated) when it's saved and not running, and more
> importantly, don't power cycle any of the hardware attached to it
> until it's been shut down properly.

In my use case I'm thinking that I would dedicate the PCI device (SCSI
controller here) to one VM and not  move it to another VM or domain-0.
Given that assumption, it should all work pretty seamlessly, correct?

-- 
Jon Schewe
Research Scientist
Raytheon BBN Technologies
5775 Wayzata Blvd, Ste 630
Saint Louis Park, MN, 55416
Office: 952-545-5720


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