⁠6.8.3. Demonstrating virtual-machine high availability when storage networks are down (Host: non-SPM)

Previously, the Pacific host was running as the SPM. However, the role of SPM can be transferred, because it has to be filled by a running host. After Pacific had been rebooted, the Atlantic host gained the status of SPM. Therefore, in this example the Pacific host is used again, as it can now play the role of the host which is not the SPM. Before running the next procedure, migrate several virtual machines from Atlantic to Pacific.

To demonstrate virtual machine high availability when storage network is down (Host: non-SPM)

  1. As before, connect to the Pacific host via SSH. Check your available network by running the following command: 
    [root@pacific ~]# ifconfig
    Once you have determined the name of your storage network, run: 
    [root@pacific ~]# ifdown storage
[root@pacific ~]# ifdown p1p1
    You have now shut down the network between the Pacific host and the ISCSI-share storage. If new data is being written onto the virtual machine's disk, the virtual machine detects that the storage connection has been lost, and pauses itself to prevent loss of data. When this happens, the Hosts tab shows that the status of the Pacific host has changed to Non Operational.
  2. Click the pacific.demo.redhat.com icon on the Tree pane to examine the virtual machines. All the virtual machines which were originally running on the Pacific host are automatically migrated to the Atlantic host. The highly available machines, which were set as high priority, are migrated before the non-highly available ones.
    When virtual machines are live migrated, they do not experience any downtime. In rare cases, they will be paused, and then continued on the host they have been migrated to.
    ⁠
    Virtual machines automatically migrated

    Figure 6.12. Virtual machines automatically migrated

When the host that holds the SPM role loses connectivity to storage, that host is fenced. VDSM is restarted on the host (restarting VDSM on the host is called "self-fencing").
When the host that runs virtual machines loses network connectivity, that host moves to non-operational status and all of the virtual machines running on it migrate to a new host.
Report a bug