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[Chuck Thier <cthier@xxxxxxxxx>]

Hey Andi,

Perhaps it would be better to re-frame the question.

What should the base functionality of the Openstack API for
backup/snapshot functionality be?

I'm looking at it from the perspective of initially providing the
capabilities that EC2/EBS currently provides (which they call
snapshots).  To me, this is the absolute base of what is needed, and
is what I am basically proposing as the idea of backups.

I also see that allowing for true volume snapshot capabilities are
desirable down the road.  The difficulty with snapshots, is that their
properties can vary greatly between different storage systems, and
thus needs some care in defining what a Nova Volume snapshot should
support.  I would expect that the different storage providers would
initially provide this support through extensions to the API.  At that
point it may be easier to find what commonalities there are, and to
find what types of features are most demanded in the cloud.

--
Chuck

On Thu, Jul 21, 2011 at 5:57 AM, Andiabes <andi.abes@xxxxxxxxx> wrote:
> I think vish pointed out the main differences between the 2 entities, and maybe that can lead to name disambiguation...
>
> Backup is a full copy, and usable without the original object being available in any state ( original or modified). It's expensive, since it's a full copy. Main use cases are dr and recovery.
>
> Snapshot represents a point in time state of the object. It's relatively cheap ( with the expectation that some copy-on-write or differencing technique is used). Only usable if the reference point of the snapshot is available (could be thought of as an incremental backup); what that reference point is depends on the underlying implementation technology. Main use case is rewinding to so a historic state some time in the future.
>
> That said, with the prereqs met, both can probably be used to mount a new volume.
> Reasonable?
>
> On Jul 20, 2011, at 5:27 PM, Chuck Thier <cthier@xxxxxxxxx> wrote:
>
>> Yeah, I think you are illustrating how this generates much confusion :)
>>
>> To try to be more specific, the base functionality should be:
>>
>> 1. Create a point in time backup of a volume
>> 2. Create a new volume from a backup (I guess it seems reasonable to
>> call this a clone)
>>
>> This emulates the behavior of what EC2/EBS provide with volume
>> snapshots.  In this scenario, a "restore" is create a new volume from
>> the backup, and delete the old volume.
>>
>> In the Storage world, much more can generally be done with snapshots.
>> For example in most storage system snapshots are treated just like a
>> normal volume and can be mounted directly.  A snapshot is often used
>> when creating a backup to ensure that you have a consistent point in
>> time backup, which I think most of the confusion comes from.
>>
>> What we finally call it doesn't matter as much to me, as long as we
>> paint a consistent story that isn't confusing, and that we get it in
>> the Openstack API.
>>
>> --
>> Chuck
>>
>> On Wed, Jul 20, 2011 at 3:33 PM, Vishvananda Ishaya
>> <vishvananda@xxxxxxxxx> wrote:
>>> In rereading this i'm noticing that you are actually suggesting alternative usage:
>>>
>>> backup/clone
>>>
>>> snapshot/restore
>>>
>>> Correct?
>>>
>>> It seems like backup and snapshot are kind of interchangable.  This is quite confusing, perhaps we should refer to them as:
>>>
>>> partial-snapshot
>>>
>>> whole-snapshot
>>>
>>> or something along those lines that conveys that one is a differencing image and one is a copy of the entire object?
>>>
>>> On Jul 20, 2011, at 12:01 PM, Chuck Thier wrote:
>>>
>>>> At the last developers summit, it was noted by many, that the idea of
>>>> a volume snaphsot in the cloud is highly overloaded.  EBS uses the
>>>> notion of snapshots for making point in time backups of a volume that
>>>> can be used to create a new volume from.  These are not true snapshots
>>>> though from a storage world view.  Because of this I would like to
>>>> make the following proposal:
>>>>
>>>> Add a backup API to the Openstack API for Nova Volume.  This is to
>>>> provide EBS style snapshot functionality in the Openstack API.  I'm
>>>> proposing to name it backup instead of snapshot as that seems to
>>>> better describe what is happening.  It also allows room for other
>>>> storage backends to expose real snapshot capabilities down the road.
>>>>
>>>> In the case of Lunr, we would be making backups of volumes to swift
>>>> (possibly abstracted through glance in the future).
>>>>
>>>> I have started a blueprint and spec at:
>>>>
>>>> https://blueprints.launchpad.net/nova/+spec/backups-api
>>>> http://etherpad.openstack.org/volume-backup
>>>>
>>>> Please feel free to comment and contribute.
>>>>
>>>> --
>>>> Chuck
>>>>
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>>>
>>>
>>
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>