Question about the instance snapshot

Sean Mooney smooney at
Wed Nov 11 17:47:49 UTC 2020

On Wed, 2020-11-11 at 15:41 +0000, Eugen Block wrote:
> Hi,
> taking an instance snapshot only applies to the root disk, other  
> attached disks are not included.
yes this is by design. snapshot have only ever applied to the root disks
volume snap shots can be done via the cinder api in a much more efficent way.
>  I don't have an explanation but I  
> think it would be quite difficult to merge all contents from different  
> disks into one image.
well not just diffuclt it would be very in efficnt to use one image and unexpected
to have an image per volume.

its nut not in the scope of the nova snapshot api to do anything other then the root
disk. volume snapshot realy should jsut be done on the backing store without transfering
any data to glance and just using glance to store teh metadata.

if we were to have qemu snapshot the volume it would have to potentialy copy a lot of data
or invoke the existign volume snapshot apis and we have said in the past that nova should not proxy
calls to other service that can be orchestrated externally.

>  If this is about backup and not creating new  
> base images and your instances are volume-based you could create  
> cinder snapshots of those volumes, for example by creating  
> consistency-groups to have all volumes in a consistent state.
> If this is more about creating new base images rather than backups and  
> you have an instance with its filesystem distributed across multiple  
> volumes it would probably be better to either move everything to a  
> single volume (easy when you're using LVM) or resize that instance  
> with a larger disk size. There are several ways, it depends on your  
> actual requirement.
> Regards,
> Eugen
> Zitat von Henry lol <pub.virtualization at>:
> > Hello, everyone
> > 
> > I'm wondering whether the snapshot from the instance saves all disks
> > attached to the instance or only the main(=first) disk, because I can't
> > find any clear description for it.
yes it is only for the root disk.
> > 
> > If the latter is true, should I detach all disks except for the main from
> > the instance before taking a snapshot, and why doesn't it support all
> > attached disks?
> > 
> > Thanks
> > Sincerely,

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