[Engine-devel] 'deactivate' disk - what's the use case?

[Yaniv Kaul]

On 06/17/2012 12:44 PM, Simon Grinberg wrote:
>
> ----- Original Message -----
>> From: "Yaniv Kaul" <ykaul at redhat.com>
>> To: "Livnat Peer" <lpeer at redhat.com>
>> Cc: engine-devel at ovirt.org
>> Sent: Tuesday, June 12, 2012 2:14:00 PM
>> Subject: Re: [Engine-devel] 'deactivate' disk - what's the use case?
>>
>> On 06/12/2012 12:47 PM, Livnat Peer wrote:
>>> On 12/06/12 12:40, Yaniv Kaul wrote:
>>>> On 06/12/2012 12:34 PM, Itamar Heim wrote:
>>>>> On 06/12/2012 12:25 PM, Yaniv Kaul wrote:
>>>>>> I'm wondering what's the usefulness of having dual action of
>>>>>> attach +
>>>>>> activate to get a disk properly attached and working in a VM
>>>>>> (and the
>>>>>> deactivate and detach counterparts).
>>>>>>
>>>>>> The only reason I can think of is that we've annoyed the user by
>>>>>> this
>>>>>> useless dual action when working with storage domains in a data
>>>>>> center
>>>>>> for ages, and we wish to remain consistent and annoy the user in
>>>>>> the
>>>>>> disks scenario as well, but there may be a reason I'm not aware
>>>>>> of.
>>>>> deactivated is like having a disk in offline, or hot unplugging
>>>>> when
>>>>> you still want to retain it in the context of the vm
>>>>> configuration
>>>> I understand that, I just argue it's quite useless (offline can be
>>>> done
>>>> from within the guest OS),
>>> You can deactivate the disk if for some reason it blocks the guest
>>> from
>>> starting. I think that if the disk not accessible the VM won't
>>> start and
>>> then you can deactivate the disk and start the VM.
>> You can also detach it to get the same effect with one less click of
>> a
>> button or an API call.
> And then if you did it manually for 20 VMs as a temporary measure, you'll have to re-attach it to the VMs. Will you remember to which VM you should attach each of your floating disks? You may have to now consult event log.
> (And in any case you'll need better search capabilities on disk then what you have now)

I still fail to see what the common use case for 
'deactivate-but-not-detach' is.
I assume the description for the disk is automatically filled by engine 
when the disk is created attached to the VM. I'm 99.9% my assumption is 
naive and I'll open a RFE for it...
Y.

>
> There are use cases to have an off-line disks, the issue is how not to annoy the user.
> I think I've suggested in the past that by default:
> Attach = Attach + set_Online
> Detach = set_offline + Detach.
> Unless explicitly stated otherwise by the user.
>
> Thus you do not annoy the user but still maintain the functionality.
>
>
>> Y.
>>
>>>
>>>> does not work that way in physical hardware
>>>> (offline is a logical action within the OS), has very little value
>>>> to
>>>> the RHEV Admin (unless he's paranoid and afraid that the disk will
>>>> become float and someone else would 'steal' it from his VM) and is
>>>> annoying to require multiple actions.
>>>> Y.
>>>>
>>>>>> TIA,
>>>>>> Y.
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