Storage Virtualization: Multi-part series at IBM

Barry Whyte, has been writing a decent looking series on storage virtualziation:

The whole concept of virtualizing your storage network is a disruptive one. It doesn't matter which approach
you choose, it radically changes not only the way your storage administrator thinks about his job, but also the very fundamentals of how and where things are done. Once you have an abstraction device sitting in the middle of the SAN between your hosts and your storage, or even your storage and storage, the rules have changed.

I'm sure most readers are aware of the three main approaches in use today, for more detailed explanations, google is great. However while all these approaches provide in essence the same basic 'Cornerstones of Virtualization' there are some interesting side affects with some or all approaches.

• Network Based - Appliance
  
  The device is a SAN appliance that sits in the data-path and all I/O flows through the device. The device is both target and initiator. It is the target of I/O requests from the host perspective and the initiator of I/O requests
  from the storage perspective. The redirection is performed by issuing new I/O requests to the storage.
  
  
• Switch Based - Split-path
  
  The device is usually an intelligent switch that intercepts I/O requests on the fabric and redirects the frames to the correct stroage location. The actual I/O requests are themselves redirected.
  
  
• Controller Based
  
  The device is a storage controller that provides an internal switch for external storage attachment. Here the storage controller intercepts and redirects I/O requests to the external storage as it would for internal storage. (I'm not sure if USP actually re-generates new I/O requests or simply forwards to original I/O - maybe someone can enlighten me)

• 
  

Check out part1, part2, part3 and part4.