In this introduction to hypervisor convergence, Keith Townsend presents the potential benefits and drawbacks to hyper-converged systems.
Software vendors are trying to make the transition from hypervisors with only direct attached storage (DAS) to full-feature storage area networks (SANs) as frictionless as possible. Vendors such as VMware, EMC, and HP are offering software that allows enterprise organizations to build their own hyper-converged infrastructures using the hypervisor as a base.
There is a significant appeal to building your own hyper-converged infrastructure. If your existing hardware is on the vendor's hardware compatibility list (HCL), you could possibly build a high-performing SAN with the DAS in your existing environment, and the only real cost would be the software licensing for the virtual SAN software.
What is virtual SAN software?
With the exception of VMware's VSAN, which runs in the kernel of vSphere 5.5 or later, virtual SAN software leverages some type of virtual SAN appliance (VSA). A VSA is a virtual machine (VM) that provides storage controller functionality to your hypervisor cluster. The raw, DAS of the physical node is provisioned to the VSA. The group of VSAs combines to create the virtual SAN.
The exception is VSAN. VMware leverages its access to the vSphere kernel to place the storage services within the vSphere code directly, allowing its solution to be fully integrated into vSphere. The fact that vSphere 5.5 or later is required may or may not be an issue for your environment.
The possible pros and cons of integration
While hyper-converged solutions allow you to simplify storage management, there's still the journey associated with getting a working and supported array. The value of traditional enterprise storage is in the engineering associated with the hardware and software -- these traditional systems are engineered to integrate the hardware and software. Likewise, the value of manufactured appliances is the engineering involved with the physical appliance.
Vendors commonly refer to this type of solution as hypervisor-converged due to the reliance on the hypervisor platform for the infrastructure. With this general approach, you do lose advantages of tightly coupled systems.
In hypervisor-converged systems, engineers have to hunt for configurations that are supported by the software vendor; this can make the overall procurement of hypervisor-converged systems a bit more work than a pre-manufactured solution.
Compared to traditional arrays, support is something to consider as well. A disadvantage with the hypervisor-converged approach is a single "throat to choke" for support. If there are disk-related hardware issues, you must call your server vendor. If the hardware vendor determines the hardware is working fine, you must call the software vendor for support. Don't be surprised if you end up with both the hardware and the software vendors on the phone to support your virtual SAN issues.
Software is quickly becoming the major enabler in the enterprise data center. As a result, smaller environments that have limited operations are seeing capabilities that were once reserved for larger organizations trickle down into their space.
Hypervisor-converged systems are not marketed as replacements for Tier 1 storage arrays. Virtual SAN vendors have found the SMB market is a strong target audience, while larger enterprises may leverage the approach for virtual desktop infrastructure (VDI) and test/development workloads. As these systems are battle tested, you'll find more enterprises taking the chance on hypervisor-converged systems.
As hyper-converged vendors continue to make a case for their systems, it might create a halo effect for hypervisor-converged systems and relieve some of the stigmas associated with enterprise SAN storage when it comes to cost and complexity.