What you will learn: This tip outlines three approaches to storage virtualization available today, along with some benefits, caveats and some examples of each.
In-band/symmetric 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.
- Characteristics: In-band/symmetric storage virtualization uses x86-based software or proprietary hardware and software storage systems, and appears as a target to host servers and as an initiator to storage devices. This is the most common form of storage virtualization.
- Benefits: No host agents, relative ease of deployment, caching can help performance, flexibility.
- Caveats: Potential performance bottleneck being in the data path.
- Look for: Ability to scale and interoperability without adding complexity, cost or instability to your environment.
- Examples: Traditional storage systems, appliances such, as IBM SVC, FalconStor Software Inc., DataCore Software Corp.
Out-of-band/asymmetric storage virtualization
Out-of-band storage virtualization devices sit outside the data path between the host and storage, and require additional software in the host.
- Characteristics: Out-of-band/asymmetric storage virtualization can reduce performance bottlenecks associated with in-band storage virtualization. However, it requires the agent and meta data controller to coordinate access to storage devices -- adding to the complexity of storage virtualization.
- Benefits: Potential improved performance for scaling.
- Caveats: Fading in favor of split-path.
- Look for: Vendor and solution stability and viability in the absence of going in-band or split-path.
- Examples: LSI StoreAge
Split-path storage virtualization
Split-path storage virtualization is a hybrid of the in-band and out-of-band architectures.
- Characteristics: Split-path storage virtualization utilizes a storage services module or adapter in a switch or appliance combined with software.
- Benefits: Increased flexibility in deployment while eliminating bottlenecks in the data path.
- Caveats: Vendor lock-in rests with whose software you chose, still maturing.
- Look for: Vendor stability, coexistence and scalable solution with support for different hardware and software combinations.
- Examples: LSI StoreAge, Incipient Inc., EMC Corp. Invista, Fujitsu VS9000
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 May 2007