Description
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Taking a snapshot of your virtual machine that is backed by RBD. The snapshot of the disk is saved in Glance, and it can be used to spawn new instances. 

This feature modifies the way Nova does snapshots, eliminating the need to move a copy from local ephemeral storage to the Ceph cluster, but instead making the copy operation internal to the Ceph cluster. 

old path: RBD-> local->Glance->RBD again.
new path: all data path is internal to Ceph

Currently the snapshot has to be offline (Suspend the Guest), but it cam be made live in the future.

The key user ask is the ability to use compute nodes without local storage, and snapshots are the last remaining function requiring significant local storage.

User Stories
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* As an Operator, I want to run my compute nodes without any local storage