More about Storage Virtualization

CIOL Bureau
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The storage industry has been constantly evolving over the past so many years, and is expected to continue doing so in the future as well. We saw storage technologies evolve from direct attached storage to network attached storage and eventually into a storage area network. All this has of course happened because of a heavy market demand for such storage solutions. This has led to another challenge, that of managing such a large and disparate storage infrastructure.


Storage virtualization aims to ease the administrative overhead and reduce the cost of managing such a storage infrastructure. It also aims to reduce downtime and improve the utilization of storage resources. Today, we're seeing various vendors coming out with their own interpretations and implementations of storage virtualization. This is a good sign, because it's an indicator that the technology is being taken seriously. So now it's just a matter of time before one standard emerges, and the technology becomes widely adopted.

      The Benefits
  • Since all storage resources will be in one pool, it could improve the storage utilization dramaticallyn 
  • As a follow on, better utilization of storage resources reduces the cost of storagen 
  • All complexity of the storage infrastructure is hidden, thereby making it easier to manage, thereby saving management costsn 
  • Can improve performance and reliability of the storage network

The technology 

Storage virtualization presents a logical view of physical storage by hiding the underlying complexity. It's like putting an abstraction layer between the physical storage resources and the management interface. By hiding all the physical storage complexity, the management of this entire pool of storage resources is simplified. Moreover, all this has to happen without sacrificing the performance and data integrity. Currently, all vendors have their own implementations of storage virtualization, meaning you'll find virtualization solutions for storage arrays, switching fabric, storage software, and the like. 


Storage virtualization is not a completely new technology. Take for instance, the age-old RAID or Redundant Array of Inexpensive Disks. The technology combines storage capacity of multiple disks to make the storage more fault tolerant and better performing. It's doing this by presenting one logical view of multiple physical disks to the application. It's actually storage virtualization in action. But life in the storage world has moved far ahead, so this level of virtualization doesn't help. We're in the era of high-speed networked storage, or SAN if you will, in which there are a disparate number of storage resources, possibly all of them with RAID arrays, all connected together and being accessed over a network. It's been a good move from the older, dispersed direct attached storage resources in that everything's centrally administered, but brings in its own administrative headaches. You still have to manually create logical volumes out of the shared storage pools for each server. You still have to manage all these volumes, making it a fairly complex process, and requiring a high degree of knowledge in storage management. Storage virtualization aims to automate many of these tasks and yet provide the high performance and data availability needed. It aims to simplify these challenges by helping automate various tasks, and bring intelligence into the system such that it can monitor and manage all the storage space allocated per server. 

Current implementations  

Every storage vendor, be it for hardware, software, or storage networking products have products based on their own definition of storage virtualization. This leads to a lot of confusion in the customer's mind. There's tremendous variation in the storage virtualization products and likewise for the way they have to be implemented.

Vendor Speak

Enterprises will start taking a militaristic approach to security. In 2006, enterprises will increasingly recognize the need to secure data-in-flight and data-at-rest on both disk and tape. Expect to see a majority of enterprises start to incorporate need-to-know access controls, compartmentalization, and role separation on critical systems. Encryption of tape backup data before sending tapes off site will become the norm, so also with encryption of data at rest.

IP SAN (iSCSI) will become a ubiquitous, multi-OS solution. 2005 saw iSCSI become mainstream in Windows server environments. Second generation solutions are expanding this "sweet spot" by adding high-availability support, SAN boot support for dense server environments, and performance enhancements. In 2006, iSCSI will expand support to include departmental Linux and UNIX environments, particularly for blade servers and small-to-midrange hosts. Expect to see more iSCSI deployments replacing first-generation FC SANs. Disk-to-disk backup will mature as a true complement to tape libraries. There will also be a strong trend toward the use of replication technologies to automate remote office backups.


For example, storage array vendors host virtualization on the storage controller; fabric switch vendors build it into their own products; the storage software vendors have their own definitions and implementations and so on and so forth. On top of that, each vendor claims that their implementation is the best, which makes it difficult for the customer to really decide what to choose. Add on top of that all the vendor hype that comes along with the product.

Today, different vendors offer their own proprietary solutions for storage virtualization, due to which interoperability still remains a challenge. Another objective is to overcome interoperability issues amongst different vendor products. 

The standards  

Currently, SNIA or the Storage Networking Industry Association has a definition for storage virtualization. It divides the virtualization process into three parts-what's being virtualized, where's it being virtualized, and how is it being implemented (see diagram). The first part of what is being virtualized can include block-level, disk-level, tape, file system, or file/record level virtualizations. The virtualization can be done on a host or server, the storage network, or even a storage device such as the switching fabric. Lastly, the virtualization could be in-band or out-of-band.

Lastly, while there are various implementations of storage virtualization, a lot still needs to be done. Automation of various administrative tasks is one challenge that needs to be addressed, such as creating volumes or adding a new storage array. Using a policy-based framework for managing the storage infrastructure is another challenge that needs to be addressed, such that the storage system can automatically determine what type of storage is required for which type of host. All this of course has to happen across a heterogeneous storage environment. Currently, many of these features might be available, but wouldn't be interoperable.