Installation guide

Chapter 7. Virtualization and High Availability
Various virtualization platforms are supported in conjunction with Red Hat Enterprise Linux 6 using
the High Availability and Resilient Storage Add-Ons. There are two supported use cases for
virtualization in conjunction with Red Hat Enterprise Linux High Availability Add-on.
This refers to RHEL Cluster/HA running on bare metal hosts that are themselves usable as
virtualization platforms. In this mode you can configure the cluster resource manager (rgmanager) to
manage virtual machines (guests) as highly available resources.
VMs as Highly Available Resources/Services
Guest Clusters
7.1. VMs as Highly Available Resources/Services
Both RHEL HA and RHEV provide mechanisms to provide HA virtual machines. Given the overlap in
functionality, care should be taken to chose the right product to fit your specific use case. Here are
some guidelines to consider when choosing between RHEL HA and RHEV for providing HA of VMs.
For Virtual machine and physical host counts:
If a large number of VMs are being made HA across a large number of physical hosts, using RHEV
may be the better solution as it has more sophisticated algorithms for managing VM placement
that take into consideration things like host CPU, memory and load information.
If a small number of VMs are being made HA across a small number of physical hosts, using
RHEL HA may be the better solution because less additional infrastructure is required. The
smallest RHEL HA VM solution needs two physical hosts for a 2 node cluster. The smallest RHEV
solution requires 4 nodes: 2 to provide HA for the RHEVM server and 2 to act as VM hosts.
There is no strict guideline for how many hosts or VMs would be considered a 'large number'. But
keep in mind that the maximum number of hosts in a single RHEL HA Cluster is 16, and that any
Cluster with 8 or more hosts will need an architecture review from Red Hat to determine
supportability.
Virtual machine usage:
If your HA VMs are providing services that are used are providing shared infrastructure, either
RHEL HA or RHEV can be used.
If you need to provide HA for a small set of critical services that are running inside of VMs, RHEL
HA or RHEV can be used.
If you are looking to provide infrastructure to allow rapid provisioning of VMs, RHEV should be
used.
RHEV VM HA is meant to be dynamic. Addition of new VMs to the RHEV 'cluster' can be done
easily and is fully supported.
RHEL VM HA is not meant to be a highly dynamic environment. A cluster with a fixed set of VMs
should be set up and then for the lifetime of the cluster it is not recommended to add or remove
additional VMs
RHEL HA should not be used to provide infrastructure for creating cloud-like environments due to
the static nature of cluster configuration as well as the relatively low physical node count
maximum (16 nodes)
Red Hat Ent erprise Linux 6 High Availabilit y Ad d- O n O verview
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