Understanding "vSAN Host Packet Discard Rate" and its relationship to packet drops

Products

• VMware vSAN

Issue/Introduction

In vCenter, after selecting a vSAN host and navigating to Monitor -> Performance -> Host Network, the chart "vSAN Host Packet Discard Rate" is displayed.

This article explains the meaning of this metric and clarifies how it relates to packet drops on physical NICs.

Environment

vSAN 8.x

vSAN 9.x

Resolution

The "vSAN Host Packet Discard Rate" reflects ARP resolution failures, not packet loss or physical network errors.

When a vSAN VMkernel interface attempts to communicate with an IP address that does not exist in the local vSAN subnet, the host sends ARP requests. Because no device responds to these ARP requests, the unresolved ARP entries are recorded as packet discards by the vSAN performance service.

This counter does not represent packet drops on the physical NIC, vSwitch, or VMkernel network stack.

A non-zero "vSAN Host Packet Discard Rate" simply indicates the presence of ARP resolution failures. This behavior is expected and does not indicate any network issue.

Additional Information

Summary:

• The metric is triggered only when the vSAN VMkernel interface performs ARP resolution toward an IPv4 address that has no corresponding host in the vSAN subnet. It is not correlated with physical NIC rx or tx drops.

• A host may report packet drops on the uplink with a discard rate of zero, or vice versa.

• Discard metrics represent ARP-level failures, whereas NIC drop counters represent layer-2 or hardware-related packet loss.

• This metric does not impact vSAN object health, performance, or data path reliability.

 

• 「vSAN ホストのパケット破棄レート」 とパケットドロップとの関係を理解する