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 File Copy technology or 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 or NetApp File Copy¶
Caution
The Copy Offload tool is deprecated since Zed release. It will be removed soon. Please, prefer the method File Copy technology.
The NetApp Copy Offload tool was added in the Icehouse release, while File Copy approach in the Zed release. Both enable Glance images to be efficiently copied to a destination Cinder volume. The last was added to replace the first one.
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 and File Copy improve 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.
Note
The File Copy approach does not require any setup, the driver has the logic internally. Just disabling Copy Offload tool makes the File Copy being used.
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 and File Copy Technology Flowchart” below describes the workflow associated with the Enhanced Instance Cloning capability of the NetApp NFS driver when using the deprecated NetApp Copy Offload or File Copy technology.
Figure 5.1. Enhanced Instance Creation with NetApp Copy Offload Tool and File Copy Technology 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.
This document is licensed under Apache 2.0 license.