Benefits of HA
Minimize unplanned downtime and IT service disruption
Eliminate the need for dedicated standby hardware and the installation of additional software
Enable affordable uniform high availability across the entire virtualized IT environment
VMware High Availability (HA) provides easy-to-use, cost-effective high availability for applications running in virtual machines. In the event of physical server failure, affected virtual machines are automatically restarted on other production servers with spare capacity. In the case of operating system failure,
VMware HA restarts the affected virtual machine on the same physical server. The combination of VMware HA and the other availability features of the VMware vSphere platform provide organizations the ability to select and easily deliver the level of availability required for all of their important applications.
VMware HA allows IT organizations to:
Minimize unplanned downtime and IT service disruption while eliminating the need for dedicated standby hardware and installation of additional software.
Provide affordable uniform high availability across the entire virtualized IT environment without the cost and complexity of failover solutions tied to either operating systems or specific applications.
High availability (HA)-or the lack of high availability-is the key argument used against virtualization. The most common form of this argument more or less sounds like this:
"Before virtualization, the failure of a physical server affected only one application or workload. After virtualization, the failure of a physical server will affect many more applications or workloads running on that server at the same time. We can't put all our eggs in one basket!"
VMware addresses this concern with another feature present in ESX/ESXi clusters called VMware High Availability (HA). Once again, by nature of the naming conventions (clusters, high availability), many traditional Windows administrators will have preconceived notions about this feature. Those notions, however, are premature in that VMware HA does not function like a high-availability configuration in Windows. The VMware HA feature provides an automated process for restarting virtual machines that were running on an ESX/ESXi host at a time of complete server failure. Figure 1.3 depicts the virtual machine migration.
VMware HA allows companies to provide high availability to any application running in a virtual machine. With VMware HA IT organizations can:
Protect applications with no other failover option. Provide cost-effective high availability for any application running in a virtual machine. High availability solutions are often relatively complex and expensive, and as a result typically reserved for mission critical applications. VMware HA provides a cost-effective high availability solution that makes high availability possible for software applications that were formerly left unprotected.
Establish consistent "first line of defense" for an entire IT environment. Unlike other high availability solutions that are tied to specific operating systems or application and are often complex to use, VMware HA provides an easy to manage high availability solution that can be deployed easily and uniformly across heterogeneous environments.
Avoid the cost and complexity of failover solutions tied to either operating systems or specific applications by using VMware HA to provide protection with any hardware, operating system, or application running in a virtual infrastructure with minimum cost and management overhead.
VMware HA continuously monitors all virtualized servers in a resource pool and detects physical server and operating system failures. To monitor physical servers, an agent on each server maintains a heartbeat with the other servers in the resource pool such that a loss of heartbeat automatically initiates the restart of all affected virtual machines on other servers in the resource pool.
VMware HA leverages shared storage and, for FibreChannel and iSCSI SAN storage, the VMware vStorage Virtual Machine File System (VMFS) to enable the other servers in the resource pool to safely access the virtual machine for failover. When used with VMware Distributed Resource Scheduler (DRS), VMware HA automates the optimal placement of virtual machines on other servers in the resource pool after server failure.
To monitor operating system failures, VMware HA monitors heartbeat information provided by the VMware Tools package installed in each virtual machine in the VMware HA cluster. Failures are detected when no heartbeat is received from a given virtual machine within a user-specified time interval.
VMware HA ensures that sufficient resources are available in the resource pool at all times to be able to restart virtual machines on different physical servers in the event of server failure. VMware HA is easily configured for a resource pool through VMware