[libvirt] [Qemu-devel] QEMU interfaces for image streaming and post-copy block migration
Anthony Liguori
aliguori at linux.vnet.ibm.com
Tue Sep 7 16:00:45 UTC 2010
On 09/07/2010 10:39 AM, Kevin Wolf wrote:
> Am 07.09.2010 17:30, schrieb Anthony Liguori:
>
>> On 09/07/2010 10:20 AM, Kevin Wolf wrote:
>>
>>> Am 07.09.2010 17:11, schrieb Anthony Liguori:
>>>
>>>> Copy-on-read is, in many cases, a property of the backing file because
>>>> it suggests that the backing file is either very slow or potentially
>>>> volatile.
>>>>
>>>>
>>> The simple copy-on-read without actively streaming the rest of the image
>>> is not enough anyway for volatile backing files.
>>>
>>>
>> But as a web site owner, it's extremely useful for me to associate
>> copy-on-read with an image because it significantly reduces my bandwidth.
>>
>> I have a hard time believing this isn't a valuable use-case and not one
>> that's actually pretty common.
>>
> As a web site user, I don't necessarily want you to control the
> behaviour of my qemu. :-)
>
That's why I understand your argument about -blockdev and making sure
all compat features can be overridden. I'm happy with that as a
requirement.Okay, the only place I'm disagreeing slightly is that I
think an image
>> format should be able to request copy_on_read such that the default
>> behavior if an explicit flag isn't specified is to do what the image
>> suggests we do.
>>
> Maybe we can agree on that. I'm not completely decided yet if allowing
> the image to contain such a hint is a good or a bad thing.
>
It's a tough space. We don't want to include crazy amounts of metadata
(and basically become OVF) but there's metadata that we would like to have.
backing_format is a good example. It's a suggestion and it's something
you really want to let a user override.
Regards,
Anthony Liguori
> Kevin
>
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