Logical storage cloning is a technology available from both storage array vendors and hypervisor vendors, and is used to provision multiple unique copies of a given storage object (such as a LUN, volume, virtual disk, or file) by allowing each copy to be made off of a source object without the need to completely duplicate the source.
Pointer-Based Array Clones
Some storage vendors have a method for provisioning zero-cost clones of a number of storage objects ranging from entire volumes to individual LUNs and files. This cloning capability can be leveraged in conjunction with a hypervisor for some solutions, and is sometimes integrated directly into the hypervisor itself. A major advantage of hardware-based cloning is that the uniqueness of the clones is maintained within the storage controller, and the storage object clones can be permanently provisioned.
LUN and Volume Clones
When deploying storage in a dense virtual infrastructure, the ability to provide zero-cost LUN and volume clones can aid in reducing both deployment times and required storage capacity. As most cloud deployments use LUNs and volumes as shared storage pools, the ability to clone these objects works particularly well when the solution requires duplication of a large number of virtual machines.
File-level cloning provides an obvious benefit to a virtual infrastructure as it replaces cloning of a virtual machine by copying its dataset with a nearly instantaneous and zero-cost hardware clone. Hardware-based file clones provide a storage construct that is very similar to, and in some instances identical to, running block-level data deduplication against a shared storage pool.
The benefit of hardware-enabled file-level clones is that the storage savings and immediate deployment times can be made available for all applications and datasets, including production virtual servers, virtual desktops, and lab test and development.
VMware offers logical storage cloning in the form of a software-based linked clone technology. This technology is available in a number of VMware solutions including VMware View, Lab Manager, and vCloud Director.
VMware’s technology allows a single virtual machine or template to be used as the base or master image from which multiple clones can be created. As each clone is provisioned, a separate file is created which will log SCSI-level changes that are unique to that clone’s virtual disk. As this file is a SCSI change log and not a SCSI-based disk device, this technology is intended to be used for virtual machines that have a temporary or finite lifespan.