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The storage hypervisor: Virtualization is about more than the server

Implementing a separate storage hypervisor can make it easier to manage both wide-scale storage virtualization and the server virtualization environment.

When people think about storage, they think expensive hardware -- NAS arrays or massive SANs with disk arrays, switches, fibre channel (FC) cables and host bus adapters that cost more than a house. But what NAS and SAN have in common is a level of intelligence in the storage target that communicates with all the hosts. That storage intelligence is really just software running on a dedicated computer inside the array, which could certainly be virtualized and used in a storage hypervisor.

You are already using storage virtualization

If you are using server virtualization, you are already using a basic form of storage virtualization. A server virtualization hypervisor, like vSphere or Hyper-V, has its own file system designed to store virtual machines (VMs), typically called a datastore (one example is VMware's VMFS).

Each VM has at least one virtual disk file and a configuration file (detailing all the virtual hardware for that VM), and they are both in the datastores. Because all hardware for a VM is virtualized, they can easily be moved from one virtual host to another, and virtual disks can be moved from one hypervisor datastore to another. For example, if the hypervisor recognizes that one datastore is filling up or is experiencing high latency, it can move the virtual disk from one storage system to another.

Thus, if you are using server virtualization, your virtual machine storage is already virtualized and your server hypervisor is already performing some level of storage hypervisor functionality. However, a storage hypervisor is more than just storage virtualization.

Storage hypervisor explained

Storage hypervisors can run on dedicated storage appliances, inside virtual machines, or inside a virtualization hypervisor.

More on the storage hypervisor and storage virtualization

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Managing storage for virtual servers

Implementing block virtualization to virtualize storage

Storage virtualization solutions at the array or in the network

Just as server virtualization abstracts and containerizes the guest OS from the underlying hardware, storage virtualization abstracts away the storage data from a particular type of storage hardware. In other words, the server using the blocks of data or files doesn't know or care where that data is located.

Once storage is virtualized, a storage hypervisor can manage it. The storage hypervisor has the ability to manage virtualized storage across various types of infrastructures, including Network File Systems (NFS), iSCSI and FC. Thus, if the FC SAN was running out of space, the storage hypervisor could move the virtualized storage to the iSCSI or NFS array. Besides portability, the storage hypervisor offers improved storage availability, performance and flexibility. Storage hypervisors may also offer features like data protection and replication.

Integrating the storage hypervisor and the server hypervisor

A storage hypervisor is most powerful when it is integrated with your server virtualization hypervisor. Once these hypervisors are integrated, statistics can be shared, quality of service policies for virtual machines can be accommodated and virtual machine storage can be intelligently managed. Therefore, while server virtualization hypervisors include some level of storage hypervisor, a separate storage hypervisor can mean better server virtualization performance.

State of the storage hypervisor

In the past, storage hypervisors were expensive, dedicated appliances that fit between servers and storage arrays, offering storage portability. One of the first was IBM's SAN Volume Controller (SVC), which cost about $100K five years ago. While that is still an option, there are now many storage hypervisor options, including:

While implementing a storage hypervisor may not right for everyone today, the technology is worth investigating now. It's only a matter of time before storage hypervisors are the default in every storage design.

About the author: David Davis is the author of the bestselling VMware vSphere video training library from Train Signal. He has written hundreds of virtualization articles on the Web and is a vExpert, VCP, VCAP-DCA, and CCIE #9369 with more than 18 years of enterprise IT experience. His personal website is

This was last published in April 2012

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