NetApp has long been a storage company that provides best in class appliances and storage disk shelves. NetApp is known for delivering systems and solutions with the highest levels of reliability, serviceability and manageability, and enabling scaling to multiple petabytes of data on a single system.

One of NetApp’s core strengths has been the granular management of physical disks. Disks can be provisioned to suit specific applications. The RAID layer provides disk-based reliability with RAID groups that consist of data, parity and spare disks and can help rapidly reconstruct disk read/write operations in case of disk failures. The RAID layer also performs disk maintenance such as hot spare or disk replacements on failures by managing disks individually.

Enter Software-Defined Storage

ONTAP Select provides the same data management features as traditional NetApp appliances along with all the benefits of a software-defined infrastructure. One core benefit is with providing the same deployment agility as cloud-based hyperscalers to quickly provision a storage infrastructure at scale and manage and orchestrate infrastructure using tools such as ONTAP Deploy. Another benefit is with the flexibility of deployment on commodity hardware.


To date, ONTAP Select has leveraged hardware RAID controllers to provide RAID functionality at the datastore level and did not have a RAID layer like the traditional appliances. A hardware RAID controller manages all the disk groupings, and failure management but all of this is done “under the hood”.


ONTAP Select is software-centric and provides a high level of storage abstraction. However, it also has some specific requirements with regards to the use of the hardware RAID controller:

  • ONTAP Select requires that all the disks are controlled by a hardware RAID controller such that they appear as datastores. This greatly reduces the flexibility and limits the visibility of disk-application relationships and thus limits any kind of planning with disk usage
  • Storage Administrators demand better control and segmentation of their storage resources. They want more flexibility. Administrators want to manage and allocate storage at a more granular level, enabling utilization improvements
  • Hardware RAID controllers also do not commonly support the use of key newer interfaces such as NVMe

Software RAID on ONTAP Select

Software RAID on ONTAP Select which is now available provides a great compromise between being a pure hardware-based storage appliance and being a heavily abstracted SDS product. Software RAID provides all the RAID functionality within the ONTAP Select software stack.


Some of the primary benefits of Software RAID are:

  • Software RAID provides more visibility at an individual disk level, allowing for tasks like effectively partitioning it between two different Select instances each requiring their own disk characteristics
  • It provides flexibility in provisioning such that disks can be allocated to suit the specific application’s needs, especially in a mixed disk configuration. For example, one application needs a set of SSD disks to be allocated for use with workloads that demand a higher throughput. Another application just has a need for backups in a secondary storage use-case and can do with slower SSD disks.
  • It enables the use of low-latency media such as NVMe in the future that cannot commonly be fronted by Hardware RAID controllers.
  • Software RAID eliminates need for a Hardware RAID controller and provides more options for ONTAP Select in a wider variety of deployment use-cases such as in smaller form factors.


Figure: Comparing a Hardware RAID and Software RAID Configurations         

Software RAID gives a lot of control back to Storage administrators who know best how to provision and optimize the utilization of disks while also still bringing the unique advantages of a software-defined world such as the orchestration agility in provisioning an infrastructure quickly, and the flexibility to move VMs and corresponding workloads to work across a range of commodity hardware. Raw Device Mappings (RDMs) used with Software RAID provides ONTAP with direct and dedicated access to the disks. RDM also skips a lot of the necessary layering in virtual environments such as the Hypervisor, Operating System and the storage datastore layers, opening doors for potential performance gains.


ONTAP Select now provides both hardware and software RAID options, and thus either option can be used to suit specific requirements. With Software RAID on ONTAP Select, we bring the same flexibility and control as NetApp Storage appliances to Software-defined Storage. This feature opens a choice to provide protection either through a Software RAID layer or a hardware RAID controller and is thus unprecedented among Software-defined Storage vendors, who only provide one of the two options for RAID. NetApp understood the trade-offs and implemented a Software RAID layer that could give administrators the choice for a much improved software-defined storage management through ONTAP Select.

Jay Subramanian

Jay Subramanian has been with NetApp for 15 years and is currently the Vice President of ONTAP Product Management. During this tenure at NetApp, Jay has led product management for a variety of key areas including the WAFL file system, storage efficiency, Flash, performance, multi-tenancy and more recently on Software Defined Storage. He has been an active spokesperson for NetApp on a number of customer and partner facing forums. In his current role, his Product management team sets the direction for the FAS/ONTAP product family. Prior to NetApp, Jay’s career included engineering and Product Management roles at Novell, Lotus/IBM, Network Associates (McAfee) and other startups. Jay also holds a MS in Electrical Engineering from the University of Texas and is also an alum of the Haas School of Business (UC Berkeley)

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