By using several configuration parameters Network I/O Control allocates bandwidth to traffic from basic vSphere system features.

Allocation Parameters for System Traffic

Parameter for Bandwidth Allocation

Description

Shares

Shares, from 1 to 100, reflect the relative priority of a system traffic type against the other system traffic types that are active on the same physical adapter.

The amount of bandwidth available to a system traffic type is determined by its relative shares and by the amount of data that the other system features are transmitting.

For example, you assign 100 shares to vSphere FT traffic and iSCSI traffic, while each of the other network resource pools has 50 shares. A physical adapter is configured to send traffic for vSphere Fault Tolerance, iSCSI and management. At a certain moment, vSphere Fault Tolerance and iSCSI are the active traffic types on the physical adapter and they use up its capacity. Each traffic receives 50% of the available bandwidth. At another moment, all three traffic types saturate the adapter. In this case, vSphere FT traffic and iSCSI traffic obtain 40% of the adapter capacity, and vMotion 20%.

Reservation

The minimum bandwidth, in Mbps, that must be guaranteed on a single physical adapter. The total bandwidth reserved among all system traffic types cannot exceed 75 percent of the bandwidth that the physical network adapter with the lowest capacity can provide.

Reserved bandwidth that is unused becomes available to other types of system traffic. However, Network I/O Control does not redistribute the capacity that system traffic does not use to virtual machine placement. For example, you configure a reservation of 2 Gbps for iSCSI. It is possible that the distributed switch never imposes this reservation on a physical adapter because iSCSI uses a single path. The unused bandwidth is not allocated to virtual machine system traffic so that Network I/O Control can safely meet a potential need for bandwidth for system traffic, for example, in the case of a new iSCSI path where you must provide bandwidth to a new VMkernel adapter .

Limit

The maximum bandwidth, in Mbps or Gbps, that a system traffic type can consume on a single physical adapter.