why doesn't network disconnection cause vmware high availability to move VMs?

Posted on 2011-10-19
Last Modified: 2012-05-12
Here is the scenario: we have 3 ESX 4.1 hosts all connected to a SAN with high availability enabled (we do not have DRS). There is one VM on each host for testing purposes. Each host has 3 networks currently set up: one for the management network (has vmkernel port, vmotion enabled)), one for the iSCSI connections (vmkernel ports) and one for the LAN connections for the VMs (no vmkernel ports). Let's called them respectively mgmt-net, san-net, server-net.

The mgmt-net and server-net are physically connection to the same LAN and switch. When I reboot one of the hosts without going into maintenance mode or disconnect the network cable for the NIC the mgmt-net is on, HA kicks in and moves all VMs to an available host. That works great.

Here is the issue: if I disconnect the network cables for the NICs being used by server-net, it doesn't do anything. It just reports a disconnection and HA doesn't move the VMs to a different host. What am I doing wrong?
Question by:twinstatevdv
    LVL 5

    Expert Comment

    There is a heartbeat or keepalive setting that needs to be enabled.  Some don't want machine hard reset due to network failure as it may do more harm than good.

    LVL 116

    Expert Comment

    by:Andrew Hancock (VMware vExpert / EE MVE)
    VMware High Availability deals primarily with ESX/ESXi host failure and what happens to the virtual machines (VMs) that are running on this host. HA can also monitor and restart a VM by checking whether the VMware Tools are still running. When an ESX/ESXi host fails for any reason, all the running VMs also fail. VMware HA ensures that the VMs from the failed host are capable of being restarted on other ESX/ESXi hosts.
    LVL 116

    Expert Comment

    by:Andrew Hancock (VMware vExpert / EE MVE)
    Virtual Machine Failure Monitoring

    Virtual Machine Failure Monitoring is technology that is disabled by default. Its function is to monitor virtual machines, which it queries every 20 seconds via a heartbeat. It does this by using the VMware Tools that are installed inside the VM. When a VM misses a heartbeat, VMware HA deems this VM as failed and attempts to reset it. Think of Virtual Machine Failure Monitoring as sort of High Availability for VMs.

    Virtual Machine Failure Monitoring can detect whether a virtual machine was manually powered off, suspended, or migrated, and thereby does not attempt to restart it.
    LVL 7

    Accepted Solution

    VMware HA monitors for host failures, and uses the mgmt network for its heartbeat communication by default.  This is why an HA event occurred when you unplugged the network cables for mgmt-net.

    Unplugging the cables for the server-net does nothing because you've severed the network connection to the virtual machines on the hosts, not the hosts themselves.  The hosts are still communicating to each other through mgmt-net.

    Vm monitoring uses VMware Tools to send heartbeats to the virtual machines, and the physical network connection are not involved in that detection mechanism.  It's purely a software heartbeat to the VMware tools process inside the guest os, from the host on which that guest os resides.


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