Image metadata in etcd

Image list is stored in etcd in /vitastor/config/inode/<pool>/<inode> keys.

You can even create images manually:

etcdctl --endpoints=<etcd> put /vitastor/config/inode/<pool>/<inode> '{"name":"<name>","size":<size>[,"parent_id":<parent_inode_number>][,"readonly":true]}'

For example:

etcdctl --endpoints=http://10.115.0.10:2379/v3 put /vitastor/config/inode/1/1 '{"name":"testimg","size":2147483648}'

If you specify parent_id the image becomes a CoW clone. I.e. all writes go to the new inode and reads first check it and then upper layers. You can then make parent readonly by updating its entry with "readonly":true for safety and basically treat it as a snapshot.

So to create a snapshot you basically rename the previous upper layer (for example from testimg to testimg@0), make it readonly and create a new top layer with the original name (testimg) and the previous one as a parent.

vitastor-cli, K8s, OpenStack and other drivers also store the reverse mapping in /vitastor/index/image/<name> keys in JSON format: {"id":<inode>,"pool_id":<pool>} and ID counters in /vitastor/index/maxid/<pool> as numbers to simplify ID generation.