[ovirt-users] oVirt VM backup and restore

[Juan Hernández]

On 03/09/2017 02:10 PM, Nathanaël Blanchet wrote:
> 
> 
> Le 09/03/2017 à 12:10, Juan Hernández a écrit :
>> On 03/09/2017 11:57 AM, Gianluca Cecchi wrote:
>>> On Thu, Mar 9, 2017 at 11:39 AM, Nathanaël Blanchet <blanchet at abes.fr
>>> <mailto:blanchet at abes.fr>> wrote:
>>>
>>>
>>>
>>>      Le 09/03/2017 à 10:25, Gianluca Cecchi a écrit :
>>>>      On Wed, Mar 8, 2017 at 6:05 PM, Gianluca Cecchi
>>>>      <gianluca.cecchi at gmail.com <mailto:gianluca.cecchi at gmail.com>>
>>>> wrote:
>>>>
>>>>
>>>>
>>>>          NOTE: during the snapshot creation I see in web admin console
>>>>          the VM in paused state and also not responsive in both console
>>>>          and ssh session.
>>>>          After a couple of seconds it comes back and as a confirmation
>>>>          I see this in its messages:
>>>>
>>>>          Mar  8 17:38:57 T-ORACLE73 chronyd[616]: System clock wrong by
>>>>          19.077230 seconds, adjustment started
>>>>
>>>>          Is this expected?
>>>>
>>>>
>>>>
>>>>
>>>>      Possibly the default changed at some point in time, so that now it
>>>>      saves memory and so this implies pause of VM
>>>      Saving memory is essential in some apàplications like DB, so you
>>>      won't bypass vm pauses for such a stuff
>>>
>>>
>>> Yes, indeed, the important thing is to have an option so that you can
>>> set it True or False, depending on the VM you are saving, the
>>> application that is running isnide it and the way you want to do backup
>>> of the application.
>>> Nevertheless, RDBMS and also other applications often have some
>>> mechanism to be "frozen in a consistent state" so that you can save what
>>> you have on disk without need to save memory to have a consistent
>>> backup.
>>> Oracle for example has functionality to be put in "backup mode" where
>>> you issue "begin backup" before the snapshot and "end backup" right
>>> after snapshot completion.
>>> I see that POstgreSQL has similar functionality (not tested myself):
>>> https://www.postgresql.org/docs/9.4/static/continuous-archiving.html#BACKUP-LOWLEVEL-BASE-BACKUP
>>>
>>> and the same for other ones.
>>>
>>> Gianluca
>>>
>> Just wanted to add that freezing activity is not only important for
>> databases, but also for plain file systems. In order to do a consistent
>> backup it is important to freeze the file systems before creating a live
>> snapshot, and thaw it afterwards. oVirt does that automatically, but
>> only if the guest agent is installed and running. So, remember to have
>> the guest agent installed and running in the virtual machines that you
>> plan to backup using this mechanism.
> Very useful piece of information, so does that mean memory save feature
> not to be really useful? if so, it shouldn't be the default, so that vm
> never go into pause state unusefully.

I didn't mean that saving memory isn't useful. It is very useful, for
certain use cases. For the backup use case I think it is better to
disable it.