ERRATA: I have amended the sizing formula to include not only the Master Replica, but also the replicas. Please read second part of this article at http://myvirtualcloud.net/?p=779.
One of the great features provided by VMware View Composer is the linked cloning technology. Linked clones are dependent VMs linked to a master VM. A ‘replica’ is a copy of the Parent VM and serves as the Master VM.
Sizing storage for Linked Clones require a little bit more thought then Full Clones, as there is more to be considered. It’s necessary to take in consideration the sizes of the Master Replica, Delta Footprint, Log Files, User Data Disk and overhead.
The Delta contains only the differences from the master VM disk that are unique to the cloned VM, resulting in significant storage savings.
Let’s use the following example: 100 VMs with 20GB disk, 2GB RAM and 2GB User Data disk.
· Master Replica – 20 GB
· Delta Footprint – VM Provisioned Memory x 3 (2048 x 3 = 6144 MB)
· Maximum Log Size – 100 MB
· User Data Disk – 2048 GB
· Overhead 15%
973 GB (100 * (6144MB + 100MB + 2048MB) + 20GB + 124GB)
973 GB (n° VMs * (Delta Footprint + Log + User Data Disk) + Replica + Master Replica + Overhead)
A simplistic comparison with the same number of VMs using Full Clones would look like:
2.2 TB (100 * (20GB + 100MB + 2048MB))
2.2 TB (n° VMs * (Clone + Log + User Disk))
It’s not difficult to calculate storage consumption, but add to it Storage I/O, Datastore Sizing, Tiering ,IP storage; I wouldn’t say this is a 15 min job.
Now, If VMware introduces Thin Provisioning as a feature in View we than have a totally new scenario to analyse. The technology is already available in vSphere stack. Would it look like that?
Linked Cloning vs. Linked Cloning Thin Provisioned vs. Full Cloning Thin Provisioned
There is also Hardware Thin Provisioning at the storage layer to add to the equation.
To learn more about Linked Cloning technology refer to View Manager Administration Guide and View Architecture Design at http://www.vmware.com/support/pubs/view_pubs.html