IOVMAX

IOVMAX is a term used in the field of I/O virtualization to describe the maximum number of I/O Virtual Functions (VFs) that can be instantiated from a single Physical Function (PF) on SR-IOV capable PCIe devices. It represents a hardware capability determined by the device’s SR-IOV implementation and is part of the PCIe SR-IOV configuration that enables resource partitioning for virtualization workloads.

In SR-IOV, a single PCIe device exposes a PF plus a set of VFs that can be assigned directly to virtual machines or other software contexts. The IOVMAX value effectively sets the upper bound for how many VFs a device can support. The actual number of VFs that can be used in a system may be constrained by the device’s firmware, driver, system memory, and other platform factors. The SR-IOV capability in the PCIe configuration space typically includes a field known as Total VFs that reflects this upper limit, while the operating system may expose a separate parameter indicating the current configured VFs.

Configuration and management of IOVMAX typically involve hardware and firmware tools as well as operating system interfaces. In many environments, administrators determine the number of VFs to configure via vendor-specific utilities or BIOS/firmware settings, and in the Linux ecosystem, the number of VFs is often reflected by and controlled through sysfs attributes such as sriov_totalvfs and sriov_numvfs. The chosen value balances the need for VM isolation and performance against resource availability and management overhead.

See also: SR-IOV, PCI Express, virtualization.