A few years ago, software-defined storage might have been called storage virtualization or a highly virtualized storage system. If you search on the term software-defined storage, you will find a variety of storage and storage virtualization vendors who have renamed their offerings to fit the current software-defined technology trend.
With storage virtualization, you run into the challenge of putting an intelligent management layer in front of costly, full-featured storage systems with their own virtualization features built in, yielding high cost and potential for conflicts in control. The natural direction for this technology to move is toward an intelligent software layer sitting in front of low-cost, low-feature commodity capacity nodes. This is the direction software-defined technology is heading, and it makes sense if your shop is one that would build a storage system outside of the constraints of legacy purchases sitting around the data center.
Here are the three main forms of software-defined storage technology:
1. Controlling multivendor storage from a single console. This resembles external storage virtualization closely, and appears to be a re-branding of those same features and benefits under a more up-to-date moniker. The potential benefits of this are still there, as are the drawbacks. Newer offerings in the space have added orchestration, automation and API controls available to applications, which moves the needle in terms of what it can do, especially in a cloud or virtual server environment that can offer storage control to the application or management layer. EMC ViPR, DataCore, Atlantis USX and some iterations of IBM SVC are moving from roots in storage virtualization toward software-defined technology, offering better results from traditional storage through external influence and control.
2. Selling storage as software-only. Many next-generation storage vendors who realize their value proposition is more in software than in hardware are allowing their customers to purchase only the software, and integrate it with commodity hardware of their choice. This is especially valuable if you plan to use existing capacity or have great discounts with suppliers. It can help customers avoid paying huge markups on commodity hardware that's not substantially different from what they could purchase on their own. The downside is that customers have a bigger responsibility when it comes to architecting, testing and troubleshooting solutions compared to buying a fully integrated hardware and software combination. Most of the object storage systems on the market today, such as Scality, Cleversafe and Ceph, along with open source storage such as Nexenta or OpenStack-based options, are available in software-only configurations and describe themselves as software-defined storage.
3. Converged systems. Vendors of converged systems, like Nutanix, SimpliVity, Coho Data and others, tailor storage and server combinations to be particularly effective at running specific workloads -- generally server virtualization and orchestration. In their case, the software that defines the storage is a combination of their own internal system software, and the virtualization software it's running that gets to closely control the storage.
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