[ovirt-users] oVirt VM backup and restore

[Nathanaël Blanchet]

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.
>

-- 
Nathanaël Blanchet

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