Software Defined Storage

SDS is a class of storage solutions that can be used with commodity storage media and compute hardware; where storage media and compute hardware have no special intelligence embedded in them.  All the intelligence of data management and access is provided by a software layer. The solution may provide some or all the feature of modern enterprise storage systems like scale up and out architecture, reliability and fault tolerance, high availability, unified storage management and provisioning, geographically distributed data center awareness and handling, disaster recovery, QoS, resource pooling, integration with existing storage infrastructure, etc. It may provide some or all data access methods like file, block and object.

A generic data flow in a SDS solution is explained in the figure below:

Source : http://thenewstack.io/understanding-software-defined-storage/

VMware defines the Software-defined Storage Architecture as follows:

SDS is a new approach to storage that enables a fundamentally more efficient operational model. We can accomplish this by:

• Virtualizing the underlying hardware through the Virtual Data Plane
• Automating storage operations across heterogeneous tiers through the Policy-Driven Control Plane

Virtual Data Plane

In the VMware SDS model, the data plane, responsible for storing data and applying data services (snapshots, replication, caching, and more, is virtualized by abstracting physical hardware resources and aggregating them into logical pools of capacity (virtual datastores) that can be flexibly consumed and managed. By making the virtual disk the fundamental unit of management for all storage operations in the virtual datastores, exact combinations of resources and data services can be configured and controlled independently for each VM. 

The VMware implementation of the virtual data plane is delivered through:

• Virtual SAN – for x-86 hyperconverged storage
• vSphere Virtual Volumes – for external storage (SAN/NAS)

Policy-Driven Control Plane

In the VMware SDS model, the control plane acts as the bridge between applications and infrastructure, providing standardized management and automation across different tiers of storage. Through SDS, storage classes of service become logical entities controlled entirely by software and interpreted through policies. Policy-driven automation simplifies provisioning at scale, enables dynamic control over individual service levels for each VM and ensures compliance throughout the lifecycle of the application. 

The policy-driven control plane is programmable via public APIs used to control policies via scripting and cloud automation tools, which in turn enable self-service consumption of storage for application tenants. 

The VMware implementation of the policy-driven control plane is delivered through:

• Storage Policy-Based Management – provides management over external storage (SAN/NAS) through vSphere Virtual Volumes and over x86 storage through Virtual SAN.

Nutanix which is another player in the field of Software-defined Storage follows a similar approach but the controller here is a seperate VM on top of hypervisor and requires Nutanix hardware to implement the approach.

You can read more on software defined storage in this ebook written by Scott Lowe

Coho Data which is based out of Sunnyvale, California uses a SDN enabled data stream switch to connect the VMs to storage implemented as MicroArray Nodes containing PCIe flash and hard drives.

Data Hypervisor Software on the MicroArray virtualizes storage hardware to create a high performance, bare metal object store that scales to support different application needs without static storage tiers.

Coho Data Architecture: http://www.cohodata.com/coho-scale-out-storage-architecture