Cloud Computing vs. Virtualization & Virtual disk Storage

Virtualization is the creation of a virtual version of something such as operating systems, a server or a network resource. There is a difference between virtualization and Cloud computing. Virtualization is the part of physical infrastructure while cloud computing is a service which can be of Cloud Storage. There is also a significant cost difference between the two. For those who use virtualization faces high upfront as compare to cloud computing but can save in the long run depending on the requirements of the organization. Virtualization changed the landscape of modern data center for storage as it did for the compute. Just as physical machines were virtualized, physical storage is also abstracted in virtual disks.

In virtualization hypervisors provide same hardware environment for each virtual machine, including storage, memory and computer. VMware which is the modern hypervisor choose to emulate local physical disk drives as a way to provide storage for each VM. VMware choose the local disk drive (DAS) model as the way to expose storage to virtual machines. The unit of storage in DAS is the physical machine and the fundamental unit in virtual disk storage is VM.

Virtual disks are part of a particular virtual machine just as local disks are conceptually part of a physical computer. A virtual disk will live and die with the VM itself; if the VM is deleted, then the virtual disk will be deleted as well.

There are different kind of virtual disk storage models in use which includes

· Storage in VMware vSphere

· Microsoft Hyper-V

· Red Hat Enterprise virtualization

· Xen environments

Implementation of Virtual Disks

VMware just couldn’t only rely on a Direct Attached Storage (DAS) protocol to implement virtual disks so Storage Area Network (SAN) is also used since a SAN LUN closely resembles a local disk drive.

However, physicals LUNs have limitations. Virtualized environments consist of a number of logical computers on to a single physical server which means the number of virtualized disks on a given host will be much larger than the number of physical LUNs for a host in physical environment. The maximum number of LUNs that could be attached to a physical server was too low to support the number of virtual disks.

Moreover these virtual disks as with virtual computers must be programmed in such a way that they can be created or destroyed programmatically, however SAN was not designed to perform such operations. For these reasons, VMware chose to implement virtual disk as files in a file system (NFS) or in a distributed file system (VMFS) on SAN rather than LUNs.