Open Stack

On Mon, 13 Aug 2018 09:46:41 -0600, Chris Friesen wrote:
> On 08/13/2018 02:07 AM, Rambo wrote:
>> Hi,all
>>
>>         I find it is important that live-resize the instance in production
>> environment,especially live downsize the disk.And we have talked it many
>> years.But I don't know why the bp[1] didn't approved.Can you tell me more about
>> this ?Thank you very much.
>>
>> [1]https://review.openstack.org/#/c/141219/
> 
> 
> It's been reviewed a number of times...I thought it was going to get approved
> for Rocky, but I think it didn't quite make it in...you'd have to ask the nova
> cores why not.
> 
> It should be noted though that the above live-resize spec explicitly did not
> cover resizing smaller, only larger.

 From what I find in the PTG notes [1] and the spec, it looks like this 
didn't go forward for lack of general interest. We have a lot of work to 
review every cycle and we generally focus on functionality that impact 
operators the most and look for +1s on specs from operators who are 
interested in the features. From what I can tell from the 
comments/votes, there isn't much/any operator interest about live-resize.

As has been mentioned, resize down is hypervisor-specific whether or not 
it's supported. For example, in the libvirt driver, resize down of 
ephemeral disk is not allowed at all and resize down of root disk is 
only allowed if the instance is boot-from-volume [2]. The xenapi driver 
disallows resize down of ephemeral disk [3], the vmware driver disallows 
resize down of root disk [4], the hyperv driver disallows resize down of 
root disk [5].

So, allowing only live-resize up would be a way to behave consistently 
across virt drivers.

-melanie

[1] https://etherpad.openstack.org/p/nova-ptg-rocky L690
[2] 
https://github.com/openstack/nova/blob/afe4512bf66c89a061b1a7ccd3e7ac8e3b1b284d/nova/virt/libvirt/driver.py#L8243-L8246
[3] 
https://github.com/openstack/nova/blob/afe4512bf66c89a061b1a7ccd3e7ac8e3b1b284d/nova/virt/xenapi/vmops.py#L1357-L1359
[4] 
https://github.com/openstack/nova/blob/afe4512bf66c89a061b1a7ccd3e7ac8e3b1b284d/nova/virt/vmwareapi/vmops.py#L1421-L1427
[5] 
https://github.com/openstack/nova/blob/afe4512bf66c89a061b1a7ccd3e7ac8e3b1b284d/nova/virt/hyperv/migrationops.py#L107-L114