Theory of Operation: Enhanced Instance Creation¶

The OpenStack compute service allow creation of persistent instances. When creating a persistent instance from a disk image, the image is copied to the backing block storage volume. This copy operation is typically time and bandwidth intensive. When backed by ONTAP, the NetApp unified driver is capable of performing an enhanced instance creation.

This Enhanced Instance Creation feature is comprised of two distinct technologies, namely:

1) NetApp Flexclone technology, sometimes referred to as Rapid Cloning
2) NetApp Copy Offload tool.

The former technology is supported by Cinder volumes backed by NFS, iSCSI and FC protocols while the latter is supported only by Cinder volumes backed by NFS.

NetApp FlexClone technology¶

The NetApp FlexClone technology is leveraged to rapidly clone Cinder volumes from cached image-volumes. As said above, this technology is leveraged regardless of the underlying protocol.

NetApp Copy Offload Tool¶

The NetApp Copy Offload tool was added in the Icehouse release to enable Glance images to be efficiently copied to a destination Cinder volume. When Cinder and Glance are configured to use the NetApp Copy Offload tool, a controller-side copy is attempted before reverting to downloading the image from Glance. Copy offload improves instance provisioning times while reducing the consumption of bandwidth and CPU cycles on the host(s) running Glance and Cinder. This is due to the copy operation being performed completely within the storage cluster.

Tip

For maximum Enhanced Instance Creation performance, it is recommended to use the NetApp Copy Offload tool with NFS.

Note

The NetApp Copy Offload tool requires that:

The storage system must have ONTAP v8.2 or greater installed.
The vStorage feature must be enabled on each storage virtual machine (SVM, also known as a Vserver) that is permitted to interact with the copy offload client. To set this feature:

nfs modify -vserver openstack_vs1 -vstorage enabled

Figure 5.1, “Enhanced Instance Creation with NetApp Copy Offload Tool Flowchart” below describes the workflow associated with the Enhanced Instance Cloning capability of the NetApp NFS driver when using the NetApp Copy Offload tool.

Figure 5.1. Enhanced Instance Creation with NetApp Copy Offload Tool Flowchart¶

Note

In the second decision point in the flowchart described in the figure above, Cinder determines if the source image from Glance and the destination volume would reside in the same FlexVol volume. This can be achieved by creating a directory structure within the NFS export to segment the Glance images from Cinder volumes, and appropriately setting the filesystem_datastore_dir and nfs_shares_config.

This is not a best practice.