When a Network I/O Control profile is attached to an N-VDS, during contention the switch allocates available bandwidth according to the configured shares, limit, and reservation for each vSphere traffic type.

How Network I/O Control Works

Network I/O Control enforces the share value specified for the different traffic types only when there is network contention. When contention occurs, Network I/O Control applies the share values set to each traffic type. As a result, less important traffic, as defined by the share percentage, is throttled, granting access to more network resources to more important traffic types.

Network I/O Control also supports the reservation of bandwidth for system traffic according to the overall percentage of available bandwidth.

Network I/O Control Heuristics

The following heuristics can help with design decisions.

Shares vs. Limits

When you use bandwidth allocation, consider using shares instead of limits. Limits impose hard limits on the amount of bandwidth used by a traffic flow even when network bandwidth is available.

Limits on Network Resource Pools

Consider imposing limits on a resource pool. For example, set a limit on vSphere vMotion traffic to avoid oversubscription at the physical network level when multiple vSphere vMotion data transfers are initiated on different ESXi hosts at the same time. By limiting the available bandwidth for vSphere vMotion at the ESXi host level, you can prevent performance degradation for other traffic.

Network I/O Control Design Decisions

Based on the heuristics, this design has the following decisions.

Table 1. Network I/O Control Design Decisions

Decision ID

Design Decision

Design Justification

Design Implication

NSXT-VI-SDN-017

Create and attach a Network I/O Control Policy on all N-DVS switches.

Increases resiliency and performance of the network.

If configured incorrectly, Network I/O Control might impact network performance for critical traffic types.

NSXT-VI-SDN-018

Set the share value for vSphere vMotion traffic to Low (25).

During times of network contention, vSphere vMotion traffic is not as important as virtual machine or storage traffic.

During times of network contention, vMotion takes longer than usual to complete.

NSXT-VI-SDN-019

Set the share value for vSphere Replication traffic to Low (25).

During times of network contention, vSphere Replication traffic is not as important as virtual machine or storage traffic.

During times of network contention, vSphere Replication takes longer and might violate the defined SLA.

NSXT-VI-SDN-020

Set the share value for vSAN traffic to High (100).

During times of network contention, vSAN traffic needs a guaranteed bandwidth to support virtual machine performance.

None.

NSXT-VI-SDN-021

Set the share value for management traffic to Normal (50).

By keeping the default setting of Normal, management traffic is prioritized higher than vSphere vMotion and vSphere Replication but lower than vSAN traffic. Management traffic is important because it ensures that the hosts can still be managed during times of network contention.

None.

NSXT-VI-SDN-022

Set the share value for NFS traffic to Low (25).

Because NFS is used for secondary storage, such as backups and vRealize Log Insight archives, it is not as important as vSAN traffic. By prioritizing it lower, vSAN is not impacted.

During times of network contention, backups are slower than usual.

NSXT-VI-SDN-023

Set the share value for backup traffic to Low (25).

During times of network contention, the primary functions of the SDDC must continue to have access to network resources with priority over backup traffic.

During times of network contention, backups are slower than usual.

NSXT-VI-SDN-024

Set the share value for virtual machines to High (100).

Virtual machines are the most important asset in the SDDC. Leaving the default setting of High ensures that they always have access to the network resources they need.

None.

NSXT-VI-SDN-025

Set the share value for vSphere Fault Tolerance to Low (25).

This design does not use vSphere Fault Tolerance. Fault tolerance traffic can be set the lowest priority.

None.

NSXT-VI-SDN-026

Set the share value for iSCSI traffic to Low (25).

This design does not use iSCSI. iSCSI traffic can be set the lowest priority.

None.