What is Single Root I/O Virtualization (SR-IOV)?

Posted on Oct 19, 2023

In the realm of traditional virtualization techniques, such as network adapters, virtual machines are typically designed to simulate the presence of physical network interface cards. However, these virtual network cards are actually products of virtualization software and lack genuine hardware representation. This model results in the consumption of substantial CPU resources on the host machine to handle traffic on virtual network interfaces, ultimately leading to increased host server loads and, consequently, heightened communication latency among virtual machines.

Network Interface Card

The definition of SR-IOV by PCI SIG represents a fundamentally different approach from traditional virtualization. It provides a method for sharing the physical capabilities of PCIe I/O devices (PF: Physical Function) without the need for software emulation. The SR-IOV specification outlines the creation of virtual functions (VF: Virtual Function) for PCIe devices, with each VF being directly assignable to a virtual machine, granting each virtual machine access to unique hardware resources. As a result, SR-IOV achieves the individual allocation and utilization of devices, enabling direct hardware access by virtual machines and a significant performance enhancement.

Network Interface card

What is SR-IOV?

SR-IOV, Single Root I/O Virtualization, is a hardware specification and technology that enables a single Peripheral Component Interconnect Express (PCIe) device to be shared among multiple virtual machines (VMs) while maintaining the performance and security of traditional hardware. This technology is particularly relevant in data centers and cloud environments, where virtualization is a crucial element in efficiently utilizing hardware resources.

At its core, SR-IOV allows a physical PCIe device, like a network adapter, to appear as multiple virtual PCIe devices. Each VM can then access one of these virtual functions as if it were a dedicated physical device. This feature enables a significant reduction in the overhead traditionally associated with I/O virtualization, leading to improved performance.

SR-IOV virtual channels come in two types:

  • PF (Physical Function): PF manages the physical layer channels of the PCIe device. It can be viewed as a complete PCIe device, incorporating the functional structure of SR-IOV and having the ability to manage and configure VFs.

  • VF (Virtual Function): VF represents the virtual layer channels of the PCIe device, focusing solely on I/O functions. VF instances share physical resources, and virtual machines cannot directly manage the SR-IOV NIC via VF. All VFs are derived from PF, and certain SR-IOV NIC models can support up to 256 VF instances.

In simple terms, each VF acts as a slice of the hardware resources of the physical network card, while PF serves as the coordinator for all the hardware resources of the physical network card, managing the collaboration of numerous VFs.

Network Interface card

Advantages and Functions of SR-IOV

SR-IOV offers several advantages and functions that make it a valuable technology in modern virtualized environments:

  • Improved Performance: SR-IOV significantly reduces the overhead associated with I/O virtualization, resulting in near-native performance for VMs. VMs can communicate directly with the physical device, bypassing the virtualization layer.

  • Reduced CPU Utilization: Traditional virtualization methods involve extensive CPU processing for I/O operations. SR-IOV offloads these tasks to the hardware, reducing CPU utilization and improving overall system efficiency.

  • Enhanced Security: SR-IOV ensures strong isolation between VMs sharing the same physical device. Data remains isolated and secure, as if each VM had a dedicated hardware device.

  • Quality of Service (QoS): SR-IOV allows administrators to allocate dedicated virtual functions to specific VMs. This feature enables the prioritization of resources and ensures consistent QoS for critical applications.

  • Resource Efficiency: By optimizing I/O operations, SR-IOV leads to better resource utilization. Fewer hardware devices are needed to achieve high performance, reducing costs and energy consumption.


In summary, Single Root I/O Virtualization (SR-IOV) is a critical technology that enhances the efficiency and performance of virtualized environments. By allowing multiple virtual machines to access a single hardware device with minimal overhead, SR-IOV offers improved performance, reduced CPU utilization, enhanced security, and efficient resource utilization, making it an essential component in modern data centers and cloud computing.

FS is committed to delivering forward-thinking solutions. In synergy with the benefits of SR-IOV virtualization, we offer network cards that fully support SR-IOV. Our product includes Intel®/Intel Based Ethernet Adapters, Mellanox® Ethernet Adapters, and InfiniBand Adapters, ensuring that you have the hardware needed to harness the full potential of this remarkable technology.

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