6.7

Table Of Contents
The total number of interrupt vectors on each ESXi host can scale up to 4096 in the case of 32 CPUs.
When the host boots, devices on the host such as storage controllers, physical network adapters, and
USB controllers consume a subset of the 4096 vectors. If these devices require more than 1024
vectors, the maximum number of potentially supported VFs is reduced.
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The number of VFs that is supported on an Intel NIC might be different from the number that is
supported on an Emulex NIC. See the technical documentation from the NIC vendor.
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If you have Intel and Emulex NICs present with SR-IOV enabled, the number of VFs available for the
Intel NICs depends on how many VFs are configured for the Emulex NIC, and the reverse. You can
use the following formula to estimate the maximum number of VFs for use if all 3072 interrupt vectors
are available for passthrough:
3X + 2Y < 3072
where X is the number of Intel VFs, and Y is the number of Emulex VFs.
This number might be smaller if other types of devices on the host use more than 1024 interrupt
vectors from the total of 4096 vectors on the host.
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vSphere SR-IOV supports up to 1024 VFs on supported Intel and Emulex NICs.
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vSphere SR-IOV supports up to 64 VFs on a supported Intel or Emulex NIC.
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If a supported Intel NIC loses connection, all VFs from the physical NIC stop communication
completely, including that between VFs.
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If a supported Emulex NIC loses connection, all VFs stop communication with the external
environment, but communication between VFs still works
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VF drivers offer many different features, such as IPv6 support, TSO, and LRO checksum. See the
technical documentation of the NIC vendor for more details.
DirectPath I/O vs SR-IOV
SR-IOV offers performance benefits and tradeoffs similar to those of DirectPath I/O. DirectPath I/O and
SR-IOV have similar functionality but you use them to accomplish different things.
SR-IOV is beneficial in workloads with very high packet rates or very low latency requirements. Like
DirectPath I/O, SR-IOV is not compatible with certain core virtualization features, such as vMotion. SR-
IOV does, however, allow for a single physical device to be shared amongst multiple guests.
With DirectPath I/O you can map only one physical function to one virtual machine. SR-IOV lets you
share a single physical device, allowing multiple virtual machines to connect directly to the physical
function.
Configure a Virtual Machine to Use SR-IOV
To use the capabilities of SR-IOV, you must enable the SR-IOV virtual functions on the host and connect
a virtual machine to the functions.
vSphere Networking
VMware, Inc. 151