Open Stack

Hi Changqian, see comments inline.

On 02/01/14 07:38, Changqian Zuo wrote:
> Hi,
>
> First time mailing to a list.
>
> I'm trying to add a RBD volume snapshot rollback operation to Cinder.
> I've just got through WSGI part of Cinder API code and have read some
> pieces of Cinder Volume. Now there is not much time for me to complete
> the whole code base (with Ceph driver) very carefully, I need some
> advice. 
>
> Is adding a Extension Controller the most suitable way to do this? How
> to deal with snapshot and volume state transformation, would it affect
> other part of Cinder codes? What parts of Cinder codes I should pay
> special attention?
>
> Many thanks.
>
> Some background information: 
>
> We're planning to use Cinder bootable volume (Ceph RBD as backend) as
> instance root disk in my company's OpenStack environment. Creating a
> volume snapshot from image, and then use this snapshot to spawn instance
> root volumes.
>
> To backup volume state, I've thought of Cinder-Backup service (still
> need to add a in-use backup for Cinder), but it takes too much space (a
> 80G volume would take at least 248G space for base backup image with x3
> Ceph replication ratio). The other way is volume snapshot, but in this
> case when restoring volume data, I have to create a new volume from
> snapshot, destroy the original instance (there's no API to change a
> instance's bootable volume), and create a new instance from new volume. 
If the you use the ceph backup driver with cinder backup (added
in Havana), it is capable of doing incremental/differential backups
so it only actually stores the data that is in use so e.g. if you have
a 80G volume with 1G of actual data, the backup volume will only be
1G on disk (x number of replicas).

You can then do a 'restore' which, again, will only transfer the actual
data.

Unfortunately, there is a bug in cinder-backup (all drivers) whereby
bootable
volumes cannot be restored, or more specifically volumes cannot be
restored as
bootable. There is currently a patch in progress to resolve this which we
hope will land during the I cycle - https://review.openstack.org/#/c/51900/

hope that helps,

Ed.
> The old volume can not be removed, for a snapshot is referencing to it
> (the snapshot must be kept). If I do this again and again, there would
> be many snapshots referencing to many different volumes, and I have to
> keep these volumes (not used elsewhere), which is a mess.
>
>
>
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