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 <cth...@gmail.com> 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 > <vishvana...@gmail.com> 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 >>> >>> _______________________________________________ >>> Mailing list: https://launchpad.net/~openstack >>> Post to : openstack@lists.launchpad.net >>> Unsubscribe : https://launchpad.net/~openstack >>> More help : https://help.launchpad.net/ListHelp >> >> > > _______________________________________________ > Mailing list: https://launchpad.net/~openstack > Post to : openstack@lists.launchpad.net > Unsubscribe : https://launchpad.net/~openstack > More help : https://help.launchpad.net/ListHelp _______________________________________________ Mailing list: https://launchpad.net/~openstack Post to : openstack@lists.launchpad.net Unsubscribe : https://launchpad.net/~openstack More help : https://help.launchpad.net/ListHelp
