NTT-EMC-Openstack

Is there any better way to use cinder public snapshot with VNX?

Asked by SamP

We are looking forward to use the feature proposed in following BP.
https://blueprints.launchpad.net/cinder/+spec/public-snapshot
In order to enhance the performance of create volume from snapshot, can we use the advantage of VNX internal copy through direct driver?
Main goal is to reduce the time for create a volume from a snapshot.

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Jeegn Chen (jeegn-chen) said : 		#1

Current implementation of create_volume_from_snapshot() of VNX Cinder Driver is using VNX internal copy (mount the snapshot to a mount point and start LUN Migration).

When the blueprint public-snapshot is ready, VNX Cinder Driver should be able to leverage the public snapshot as an image.

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Jeegn Chen (jeegn-chen) said : 		#2

Currently, the major steps includes
1. Create a mount point and attach the snapshot
2 Start a LUN Migration (which means data full copy).
3. Wait for the completion of LUN Migration
4. Return so that Cinder will mark the corresponding volume as available.

Due to the data full copy, Step 3 may take long time when the size is large.

We are considering whether to add a new option to cinder.conf. When the option is set in cinder.conf, step 3 will be removed (let the LUN Migration go ahead in the background) so that the volume can become available early.

IMHO, the major constraints are
1. Before the LUN Migration is really completed, volume attaching/detaching is possible but other operations against the volume cannot be guaranteed.
2. Without checking VNX array directly, the user will not know whether the LUN migration complete or not.

Any comments?

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