Software-defined storage: Answering frequently asked questions

Russ Fellows

A new concept and a niche product just a couple of years ago, software-defined storage has found its way into the mainstream data storage market as most storage vendors are now offering some type of software-based storage networking product.

Software-defined storage (SDS) can be difficult to understand. It's often lumped with other products under the umbrella term storage hypervisor, and there is also a hardware aspect to consider.

We asked Russ Fellows, a senior partner at Boulder, Colo.-based Evaluator Group, to step us through some of the basic concepts related to software-defined storage.

What is software-defined storage, and is it the same as a storage hypervisor?

Russ Fellows: SDS is similar in concept to other software-defined elements of the data center, such as software-defined networking (SDN).

In many respects, this transformation is more about packaging and how IT users think about and design their data centers. The reality is that storage has been largely software-defined for more than a decade, with the vast majority of features designed and delivered as software components within a specific storage-optimized operating environment.

SDS is sometimes referred to as a storage hypervisor, although the two concepts are somewhat different. Both terms are evolving, with multiple vendors using these terms for different aspects of their storage systems.

In many ways, a storage hypervisor is part of software-defined storage, with a storage hypervisor the core element of an entire storage software stack. Again, vendors apply the term differently, so its meaning is not yet standard by any means.

What benefits does software-defined storage provide?

Fellows: The primary benefit of software-defined storage is separating the hardware from the software. This provides flexibility for configuration and the ability to drive down hardware costs by substituting equivalent hardware platforms. The issue with this model is that support can become more problematic, which is why existing software stacks are often only qualified and supported on a limited set of hardware.

How much of a DIY project is it to implement SDS? Do you need special expertise?

Fellows: While separating the hardware and software provides more flexibility, and creates unique configurations, IT may find they will need to pay special attention to support. Another option is to purchase a preconfigured system through a reseller. The ability to customize a product and offer support is appealing both to resellers and many businesses and IT staffs. While it's possible for adept IT professionals to configure a system, the support issues for an in-house system may not make it a worthwhile endeavor. This is the reason we see vendors deliver SDS on pretested hardware for which they can provide support services for end users.

Who are the top software-defined storage vendors?

Fellows: As I mentioned, the technical reality is that software-defined storage has been prevalent for more than a decade, with vendors such as NetApp being among the first to offer it. Today, many of the top storage vendors, along with a number of startups, are all leveraging SDS.

Currently, the ZFS software stack is one of the most readily available SDS options, along with companies that have commercialized software stacks such as Nexenta and others. A new wave of proprietary SDS stacks is also emerging, such as those from GreenBytes and Virsto, which was acquired by VMware. Traditional vendors have also been selling software-defined storage for many years, such as IBM with SVC, NetApp and HP's SDS version of its LeftHand product, which it now calls StoreVirtual VSA.

Will the SDS vendors provide adequate support even though they don't provide the actual hardware being used?

Fellows: That's hard to say. IT must carefully examine the support plan provided by the vendor and understand what is in their control and out of their control. We expect most software-defined storage products to provide approved configurations for installation, which would mean they have tested the configurations in their lab and will support those configurations. You'll also find system vendors, like Dell, HP, IBM and Oracle releasing software-defined storage with their hardware. Again, in those cases you can expect that the hardware and software has been tested and is thus supported.

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