7.2.2. General Recommendations

  • As stated above it is recommended to upgrade both the hosts and guests to the latest RHEL packages before using virtualization capabilities, as there have been many enhancements and bug fixes.
  • Mixing virtualization platforms (hypervisors) underneath guest clusters is not supported. All underlying hosts must use the same virtualization technology.
  • It is not supported to run all guests in a guest cluster on a single physical host as this provides no high availability in the event of a single host failure. This configuration can be used for prototype or development purposes, however.
  • Best practices include the following:
    • It is not necessary to have a single host per guest, but this configuration does provide the highest level of availability since a host failure only affects a single node in the cluster. If you have a 2 to 1 mapping (two guests in a single cluster per physical host) this means a single host failure results in two guest failures. Therefore it is advisable to get as close to a 1 to 1 mapping as possible.
    • Mixing multiple independent guest clusters on the same set of physical hosts is not supported at this time when using the fence_xvm/fence_xvmd or fence_virt/fence_virtd fence agents.
    • Mixing multiple independent guest clusters on the same set of physical hosts will work if using fence_scsi + iSCSI storage or if using fence_vmware + VMware (ESX/ESXi and vCenter).
    • Running non-clustered guests on the same set of physical hosts as a guest cluster is supported, but since hosts will physically fence each other if a host cluster is configured, these other guests will also be terminated during a host fencing operation.
    • Host hardware should be provisioned such that memory or virtual CPU overcommit is avoided. Overcommitting memory or virtual CPU will result in performance degradation. If the performance degradation becomes critical the cluster heartbeat could be affected which may result in cluster failure.