6.6

WAN Deployment
Incorrect routing can prevent the active and passive nodes from connecting in a WAN environment.
Problem
The VMware Channel disconnects or fails to connect in a WAN deployment.
Cause
When the VMware Channel disconnects or fails to connect in a WAN deployment, the static route might not
be configured or might be configured incorrectly.
When vCenter Server Heartbeat is deployed in a WAN, normally the Public IP address and the VMware Channel
IP addresses cannot be in different subnets, because there usually is a single network path between the two
nodes. Configure a static route between the endpoints to route traffic in the VMware Channel.
Solution
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Refer to knowledge base article 1023026 - Creating a static route for the VMware Channel for a detailed
discussion about WAN channel routing issues, and for instructions on configuring a static route for the
VMware Channel.
MaxDiskUsage Errors
vCenter Server Heartbeat uses queues to buffer the flow of replication data from the active node to the passive
node.This configuration provides resilience in the event of user activity spikes, VMware Channel bandwidth
restrictions, or VMware Channel drops across a WAN deployment. Some types of file write activity also require
buffering as they can cause a sharp increase in the amount of channel traffic. The queues are referred to as
the send queue (on the active node) or the receive queue (on the passive node).
Send Queue
vCenter Server Heartbeat considers the active node’s send queue as unsafe because data in this queue has
not yet been replicated across the VMware Channel to the passive node and therefore could be lost in the
event of a failover. As a result of a failover caused by a hardware, operating system, or network communications
failure, some data loss is inevitable, with the exact amount depending on the relationship between available
VMware Channel bandwidth and the required data transmission rate. If the required data transmission rate
exceeds available VMware Channel bandwidth, the send queue fills. If the available VMware Channel bandwidth
exceeds the required data transmission rate, the send queue empties. This situation is most commonly seen
in a WAN environment, where VMware Channel bandwidth is restricted. In a LAN that normally has high
bandwidth on a dedicated channel, the size of the send queue is zero or near zero most of the time. On a node
not protected by vCenter Server Heartbeat, all data is technically unsafe and subject to loss if the node fails.
Receive Queue
The passive node’s receive queue is considered safe because the data in this queue already was transmitted
across the VMware Channel from the active node, and is not lost in the event of a failover, which applies all
updates to the passive node as part of the process.
90 VMware, Inc.
vCenter Server Heartbeat Administrator's Guide