[Update – 1/21/2009 – I have made a new post with a demo of the benefit of Linked clones in dev/test environments]
Linked clones. What are they and why are they important?
In virtualization, linked clones (or light clones) refer to chaining of virtual machine images from a base image to reduce the amount of storage required for snapshots and slight virtual machine variations. VMware has a nice overview of linked clones: http://www.vmware.com/support/ws55/doc/ws_clone_overview.html#wp1028798
Suppose you deploy a 20GB virtual machine image, snapshot it after making 1GB of changes and then share the snapshot with ten colleagues who deploy it. Without linked clones, the entire virtual machine image has to be copied (fully cloned) 10 times, resulting in 210GB of additional storage. Worse, if these images are not run off of central storage then they have to be copied over the network to each virtual machine host. Ouch!
With linked clones, only the new delta disk has to be created any time changes are made. So for the example above, the linked clone chain would look like this for each of the 10 users:
Base Virtual Machine (20GB) > Snapshot (1GB) > New Delta Disk (empty when first deployed)
Benefits of linked clones are the following:
- Much more efficient usage of storage and network resources
- Improved productivity because end users do not have to wait for virtual machine images to be copied (deep cloned)
When are linked clones REALLY important?
- For large virtual machine images shared between multiple users or teams.
- For configurations consisting of multiple virtual machine images.
- For virtual lab deployments without shared storage
Which lab management products are known to fully support linked clones?
- VMLogix LabManager
- VMware Lab Manager