What Is Software Defined Storage (SDS)?

Software defined storage (SDS), like software defined networks, is software used to create pools of storage composed of multiple storage devices which then appears as a single unit, with the goals of adding flexibility, diversification, and enhanced functionality of the underlying storage. In short, SDS abstracts the storage management software layer away from the hardware device, effectively emancipating these management functions from the confines of each device being managed.

SDS is particularly useful in dynamically changing circumstances. In particular, SDS makes it possible for organizations to source storage from multiple vendors and data storage types that help achieve resilience and improve data availability. With SDS software, these multiple sources can be automatically provisioned, de-provisioned, and the whole can be scaled to meet data demands by simply adding storage to the software defined system.

SDS vendors should add features that include the ability to interact efficiently and effectively between all the underlying storage components. The Storage Networking Industry Association (SNIA) defines five characteristics of software defined storage.

• Automation – Automation helps to simplify management, reduce costs, and maintain storage operations between the diverse storage make-up underpinning the software defined storage system.
• Scalability – While many systems can scale, SDS must be seamless so that storage appears infinite in theory, when capacity must increase, it must do so without hiccup.
• Standardized Interfaces – SDS must supply APIs that facilitate automations, and ultimately management, maintenance and provisioning of data storage.
• Transparency – The SDS system must allow for monitoring of storage consumption so that it can be easily managed, and can inform higher level business concerns like cost.
• Virtualized Data Path – Virtualized data paths allow block, file storage, and object storage to interface between applications.

Software-defined storage software must generally supply three features:

• a policy driven control plane,
• app-centric data services,
• and a virtualized data plane.

With these features, heterogeneous storage resources can be pooled together through abstraction and managed effectively.

Sometimes, SDS is referred to as hyperconverged infrastructure (HCI) solutions, however, HCI can refer to a wider system that can include SDS, as well as other software-define software like Software-Define Networks, yet must offer these specific capabilities to be included:

• Virtualized storage, servers, and connected networks
• Scalability of underlying storage infrastructure
• Capability of backups and recovery
• Integrated with a wide range of infrastructure hardware and software

SDS vendors can fulfill both customized and turnkey software defined storage solutions. Within these two needs, several degrees of SDS can be found, so it is advisable to compare product offerings. These are not hardline categories, but rather ones that demonstrate how SDS technology is evolving.

• SDS Software Only — The basic solution is software only packages that allow for virtualization, and optimization of underlying storage devices.
• Software Layered on Enterprise Storage Arrays — Sometimes referred to as scale-out network attached storage (NAS), these hardware devices can be grouped into logical units or clusters. They are typically geared for performance of unstructured data, and specialized to bring costs down. These may also come in the form of appliances, and are marketed as hyperconverged infrastructure (HCI).
• Cloud-based SDS — Becoming more the norm for data storage are cloud-based vendors of SDS software which requires little setup from the purchaser. These HCI tout their ability to support public, private, and hybrid cloud environments with the greatest performance.
• SDS with AI Capabilities — Found in other packages, like cloud-based SDS, are more advanced AI features. AI helps admins analyze performance and space use, which translates into understanding when capacity needs to be increased, where bottlenecks may be dampening performance, and when it's time to decommission older storage devices.
• Hyperconverged Infrastructures — While SDS is often marketed as Hyperconverged Infrastructure, HCIs do more by consolidating the advantages of virtualization, servers, storage, and networking into one package reducing complexity and subsequent administration, while eliminating compatibility issues. In comparison, SDS can be thought of as an element within an HCI ecosystem, whereas HCI is a central consolidated point of control over the entire infrastructure.

In short, software defined storage decouples storage software from its hardware allowing the upgrading and downgrading of hardware at will because software manages the underlying storage. But while this is an abstraction, SDS is not storage virtualization, and SDS is not a cloud in full. That confusion comes in because SDS shares many of the same characteristics.

Abstraction is the key characteristic that cloud, storage virtualization, and SDS share. The implementation of each is what differentiates them. Storage virtualization virtualizes storage resources, effectively pooling multiple physical resources into logical units to be treated as a single storage unit. SDS utilizes storage virtualization, but the application also shifts from the hardware the responsibilities and functionalities of deduplication, snapshots, and replication to software, hence software defined storage is a manager, in addition to a virtualizer. The cloud then applies these concepts at scale.

In this way, implementing SDS can provide those functions that were not included on some storage devices. Such is the case for older storage, which would typically not include backup and replication functions, SDS can give new purpose to older storage hardware that would otherwise be considered obsolete.

Businesses benefit in key ways from the storage abstraction provided by software-defined storage platforms.

• Ultimate Choice in Underlying Hardware — Software-defined solutions are inherently designed to be agnostic. Consequently, organizations can include any variety of vendor storage in their storage infrastructures, all managed from a central point.
• Centralized Management — SDS software is uniquely designed to make visible all storage aspects and connections between underlying storage infrastructure. This helps to clarify the entire storage system, and simplify management.
• Reduced Storage Management Costs — Storage visibility brings into focus unused space which with storage optimizations can maximize system performance. With SDS optimizations, costs can be controlled and businesses can take action to reduce expenses.
• Automation of Key Storage Management Functions — Routine and error-prone tasks that were once the responsibility of human administrators can be shifted onto automated management functions. Automated functions include storage optimizations, replication, data migrations, and backups.
• Unlimited Capacity to Scale — Because an SDS management layer is decoupled from the hardware storage, storage can be added and removed from the infrastructure pool dynamically. Theoretically, the system can scale infinitely. This beneficially also allows for aging storage to be added to the pool, gaining the functionality of the SDS management layer, and repurposing unused storage assets.

Succinctly, software defined storage software is hardware agnostic because it is a software layer and not a storage device. Hardware appliance storage, or hardware defined storage, is a whole solution that combines server and storage hardware with some management software. SDS is able to pool vendor agnostic devices into a single storage resource because it abstract out of those devices the storage management software

Software-defined Storage (SDS) solutions serve multiple use cases.

• Extended Storage Network Configurations — In the instance of remote office branch office (ROBO) configurations, SDS helps to tie branch storage together with the central infrastructure. Also, SDS is a cost-effective solution for aging branch infrastructure, rather than choosing the costly alternative of replacing existing structure with usable life left.
• Rapid Response Situations — Emergency situations may call for the deployment of multiple storage units within an emergency operational area, SDSes can rapidly aggregate these deployments when time is critical.
• Hybrid Cloud and Infrastructure Modernization — SDS can be used as a bridge for companies extending their private clouds into hybrid clouds. As well, the same bridging function can be used to help companies modernize their storage infrastructure, allowing them an easy means for cloud migration.