Every byte into the pool
by Deni Connor
What if you could somehow aggregate all your storage from any type of physical device into a single pool that could be easily accessed and centrally managed? That's the promise of virtualization.
Virtualization is an abstraction of physical storage. It masks the complexity of underlying networked storage by building a logical view of storage that is isolated from physical devices.
Virtualization software collects data from different types of devices-storage-area network, network-attached and server- or direct-attached-and gathers it into a common pool that can be managed, monitored and administered from a single console.
That sounds great in theory, but how close to reality is true storage virtualization? Today, the much-hyped technology only partially realizes its ambitious goal of unifying different storage devices.
Different vendors are approaching virtualization in different ways: Some implement virtualization on only their storage devices; others virtualize a variety of devices.
But none give users total virtualization-the ability to group all storage devices and hosts under a scalable and open virtualization engine.
"We've got to the point now where if there's a nail, you hammer it,"says Jamie Gruener, an analyst with The Yankee Group. "Everyone says they have virtualization, but what does it mean?"
Storage virtualization is implemented in three ways: on the host computer or server, on an appliance, or on the storage array. Within those classifications, vendors provide symmetrical or in-band virtualization, which is in the data path, and asymmetric virtualization or out-of-band virtualization, which is outside the data path.
In in-band implementations, a device sits in the path of data between the server and the storage devices and passes data and intelligence through to arrays attached to it. In out-of-band implementations, data passing between the server, switch or router to the storage devices is managed by the server or array.
For the past year, nearly every storage and systems vendor has touted a form of storage virtualization. Many have created virtualization software of their own; others have adopted software from other vendors; and some still are working diligently on their virtualization plans, hoping to bring out products later this year.
Virtualization is a market every vendor wants to get their hooks into because of its promise of making access to data easier and simpler to administer.
Virtualization of SAN or NAS devices is most common; some virtualization software claims to throw both into the pool at once. And vendors most often take an approach that depends on the type of software or hardware they manufacture. For instance, EMC and Network Appliance say they each virtualize the disks that reside in their storage arrays, but not across product lines.
Of the seven largest storage system and storage vendors-Hewlett-Packard, Compaq, EMC, Sun, Network Appliance, IBM and Hitachi Data Systems-only a few have completely spelled out their virtualization strategies.
Beyond the Big Seven, a number of start-ups have come out with virtualization software. Three of the most successful-DataCore, FalconStor and Vicom-offer virtualization software that is installed on industry-standard Intel servers, and sold to systems and hardware vendors for redistribution
IBM and Fujitsu-Softek offer DataCore's SANsymphony; StorageTek and MTI use FalconStor's IPstor software, while Sun uses Vicom's Storage Virtualization Engine in its new StorEdge 6900.
A variety of other established storage vendors and a few start-ups such as TrueSAN and LeftHand Networks also offer virtualization software (see graphic, above).
Storage virtualization is hot territory. It promises to make the management and acquisition of storage simple and easy for IT, letting users shift storage around within the pool where they need it, while maximizing their investment.