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Storage virtualization functionality, including aggregation (pooling), transparent data migration, heterogeneous replication and device emulation, can be implemented at the host server in the data path on a network switch blade or on an appliance, as well as in a storage system. The best location to implement storage virtualization functionality depends in part on your preferences, existing technologies and objectives for deploying storage virtualization.
You may find that some applications and their storage requirements are best suited for a combination of technologies to address specific needs and requirements. This can include some applications using in-band storage virtualization appliances or storage system based storage virtualization while others use split-path fast-path control path network-based functionality.
Many debate the architecture advantages of in-band (in the data path) vs. out-of-band (out of data path with agent and metadata controller) or split path (hybrid of in-band and out-of-band). Another discussion area is around host software based vs. in the network on an appliance or storage services module blade or in a storage system. Figure-2 details the three architecture options for implementing storage virtualization:
The in-band approach involves the virtualization functionality sitting between the host server and storage devices and has been a popular approach used by appliances and traditional storage systems. Granted, Figure-2 is a pretty simple and basic example. A real-world deployment could have switches as part of the data path between servers and virtualization device, as well as switches between the virtualization device and storage.
Consider the following when deciding what will work best for your environment:
There are many different approaches to implement and deploy storage virtualization functionality to meet various requirements. Which one is best for you is going to be the one that meets your specific requirements and may vary by your different tiers of storage and applications. Compare and contrast the various approaches, and you be the judge as to what is applicable for your specific needs.
About the author: Greg Schulz is founder and senior analyst with the IT infrastructure analyst and consulting firm StorageIO Group. Greg is also the author and illustrator of Resilient Storage Networks (Elsevier) and has contributed material to Storage magazine and other TechTarget venues.
This was first published in April 2007