1. The act of abstracting, hiding, or isolating the internal function of a storage (sub) system or service from applications, compute servers or general network resources for the purpose of enabling application and network independent management of storage or data.
2. The application of virtualization to storage services or devices for the purpose of aggregating, hiding complexity or adding new capabilities to lower level storage resources.
   Storage can be virtualized simultaneously in multiple layers of a system, for instance to create HSM like systems.

Hu Yoshida, the CTO of Hitachi Data Systems, explained here..

See also Storage virtualization Wikipedia page here..

Three types of virtualization solutions:
Appliances: IBM SVC, FalconStor IPStor, DataCore SANsymphony, StoreAge SVM.
storage array systems: HDS TagmaStore, Sun StorEdge 6920
switch-based solutions: EMC Invista.

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1. IBM SVC (SAN Volume Controller)

IBM SAN Volume Controller (SVC) is a block storage virtualization appliance; designed to combine capacity from different storage systems, help provide common copy functions and enable data movement without server disruption, while supporting management of diverse storage from a single point.

more here..

2. EMC INVISTA

Go to EMC

3. SUN
# Sun StorageTek 9990V System
The Sun StorageTek 9990V is the industry's most reliable, scalable, and highest performing storage system. The 9990V delivers enterprise-class functionality, integrated storage virtualization, thin provisioning, logical partitioning, and universal replication. This simplifies storage management while reducing overall costs without sacrificing mission-critical availability.

# Sun StorageTek 9985V System
The Sun StorageTek 9985V delivers all the benefits of the StorageTek 9990V in a more flexible, modular package. With datacenter-class functionality, embedded heterogeneous virtualization, and dynamic provisioning, the StorageTek 9985V improves storage management, efficiency, and availability while reducing costs.

# Sun StorageTek 9990 System
The Sun StorageTek 9990 is an enterprise-class disk system with innovative capabilities that allows you to virtualize internal and external heterogeneous storage in a single system?improving flexibility and reducing your total cost of ownership.

# Sun StorageTek 9985 System
The Sun StorageTek 9985 system delivers breakthrough storage technologies to organizations or departments that don't need the full scalability of the StorageTek 9990 system. Like the 9990, this system provides you with full virtualization capabilities allowing you to simplify storage management and fully optimize your storage capacity.

SUN StorEdge 9985 is the same as NSC55
SUN StorEdge 9990 is the same as Tagmastore

More here..

4. HDS (Hitachi Data System)

HDS has introduced a mid-range version of Tagmastor, the NSC55. HP OEMs TagmaStore NSC55 as XP10000 and TagmaStore USP as XP12000.

5. HP

XP12000 (Disk Array+ Virtualization) = same as HDS TagmaStore
XP10000 (Disk Array Only) = same as HDS NSC55

See also: The State of Virtualization by Nick Triantos

Aloha Open Systems Storage Guy,

What’s your take on virtualization? VSAN from Cisco, SVC from IBM? What other virtualization products are available from other vendors?

Thanks,
John

Cisco VSANs and IBM's SVC are different things for certain :)

The VSAN allows you to create multiple logical fabrics within the same switch- you tell it what ports are part of what SAN, and you can manage the fabrics individually. It's especially useful if you're bridging two locations' fabrics together for replication or something because it allows you to do "inter VSAN routing" if you have the right enterprise software feature. That would allow you to have two separate fabrics whose devices can see each other, but if the link between the sites fails (which is more likely than a switch failure), you won't have the management nightmare of having to rebuild the original fabric out of two separated fabrics when the link comes back. VSANs are also commonly used to isolate groups of devices for the purpose of keeping those devices logically separated from parts of the network they'll never need to interact with.

IBM's SVC is a different technology that is supposed to consolidate multiple islands of FC storage. It's essentially a Linux server cluster that you place between your application servers and the storage. It allows you to take all the storage behind it and create what they call "virtual disks"- essentially a LUN that's passed to a server but contains multiple raids (possibly from multiple controllers). This gives you the option of striping your data across more spindles than you would be able to normally, and allows you to do dynamic thin provisioning when your datasets grow.

The only downside of the Cisco VSAN technology I can think of is its cost- it's bloody expensive compared to a cheap low end solution, and for anything less than a 50 device FC fabric, I would questionable whether it's worth it. There is an alternative from Brocade/McData they call LSAN, however I am not as familiar with it. I have been told that it's slightly less complicated, but harder to manage, and doesn't have the full feature-set of Cisco.

The downside to the IBM SVC is that you create latency for all your disk reads- every time a server needs to perform a write, it has to go through the Linux cluster first. It has a much larger cache than most controllers, so there's a better chance that the data you're looking for is already there, but if it's not, your read performance might suffer a little because of the extra few milliseconds. The advantage is that you can now use incredibly cheap controllers with tiny amounts of cache, and it allows you to migrate data from any manufacturer's device to any other manufacturer's device without interrupting your servers. Under a virtualized environment like this, an older DS4300 like you have will perform pretty much on the same level as a more expensive DS4800 or EMC CX3-80 (assuming the same number of drives) because you don't really use the cache of the underlying system. Another advantage of the SVC is that most FC storage controllers charge you either one time or over time for the number of servers you're planning to connect to them. IBM charges a "partition license" fee for LUN masking, and EMC charges a "multipath maintenance" tax. Either way, the multipath drivers for SVC are free, and it only needs one partition from the controller, so you might be able to save money that way.

Did you have any specific questions about these topics you want more detail on?

Also, one of the new bloggers in the storage world- Barry Whyte- focuses on IBM SVC. He just started, but his blog will hopefully become a real resource for people with IBM storage virtualization on their mind.