Software-defined storage

Software-defined storage (SDS) is a marketing term for computer data storage software for policy-based provisioning and management of data storage independent of the underlying hardware. Software-defined storage typically includes a form of storage virtualization to separate the storage hardware from the software that manages it.^[1] The software enabling a software-defined storage environment may also provide policy management for features such as data deduplication, replication, thin provisioning, snapshots and backup.

SDS hardware may or may not also have abstraction, pooling, or automation software of its own. When implemented as software only in conjunction with commodity servers with internal disks, it may suggest software such as a virtual or global file system. If it is software layered over sophisticated large storage arrays, it suggests software such as storage virtualization or storage resource management, categories of products that address separate and different problems. If the policy and management functions also include a form of artificial intelligence to automate protection and recovery, it can be considered as intelligent abstraction.^[2] Software-defined storage may be implemented via appliances over a traditional storage area network (SAN), or implemented as network-attached storage (NAS), or using object-based storage. In March 2014 the Storage Networking Industry Association (SNIA) began a report on software-defined storage.^[3]

Software-defined storage Industry

VMware used the marketing term "software-defined data center" (SDDC) for a broader concept wherein all the virtual storage, server, networking and security resources required by an application can be defined by software and provisioned automatically.^[4][5] Other smaller companies then adopted the term "software-defined storage", such as Coraid (defunct since 2015).

Based on similar concepts as software-defined networking (SDN),^[6] interest in SDS rose after VMware acquired Nicira for over a billion dollars in 2012.

Data storage vendors used various definitions for software-defined storage depending on their product-line. Storage Networking Industry Association (SNIA), a standards group, attempted a multi-vendor, negotiated definition with examples.^[7]

Characteristics

Characteristics of software-defined storage may include the following features:^[8]

• Abstraction of logical storage services and capabilities from the underlying physical storage systems, and in some cases pooling across multiple different implementations. Since data movement is relatively expensive and slow compared to computation and services (the "data gravity" problem in infonomics), pooling approaches sometimes suggest leaving it in place and creating a mapping layer to it that spans arrays. Examples include:
  • Storage virtualization, the generalized category of approaches and historic products. External-controller based arrays include storage virtualization to manage usage and access across the drives within their own pools. Other products exist independently to manage across arrays and/or server DAS storage.
  • Virtual volumes (vVols), a proposal from VMware for a more transparent mapping between large volumes and the VM disk images within them, to allow better performance and data management optimizations. This does not reflect a new capability for virtual infrastructure administrators (who can already use, for example, NFS) but it does offer arrays using iSCSI or Fibre Channel a path to higher admin leverage for cross-array management apps written to the virtual infrastructure.
  • Parallel NFS (pNFS), a specific implementation which evolved within the NFS community but has expanded to many implementations.
  • OpenStack and its Swift, Ceph and Cinder APIs for storage interaction, which have been applied to open-source projects as well as to vendor products.
• Automation with policy-driven storage provisioning with service-level agreements replacing technology details. This requires management interfaces that span traditional storage-array products, as a particular definition of separating "control plane" from "data plane", in the spirit of OpenFlow. Prior industry standardization efforts included the Storage Management Initiative – Specification (SMI-S) which began in 2000.
• Commodity hardware with storage logic abstracted into a software layer. This is also described as a clustered file system for converged storage.

See also

• Software-defined networking
• Software-defined data center
• OpenSDS

References