The benefits -- and limitations -- of VMware High Availability

VMware High Availability (VMHA) is a key disaster recovery tool, enabling failover of virtual machines to another physical host in a cluster -- as well as VM monitoring. But it has some limitations compared with other fault tolerance technologies.

VMware's High Availability (VMHA) provides high availability to any guest operating system at a potentially much lower cost than other HA options (as you don't have to pay per virtual machines [VMs] or per server; VMHA is included in the price of vSphere).

The pros of VMHA

VMware HA works by moving all virtual machines that run on a failed ESX server to another ESX server in the same failover cluster and restarting those VMs. A new feature of VMHA enables server virtualization administrators to monitor VMs that run in a virtualized environment for guest operating system failures. If a guest OS fails, VMHA can even restart that VM on another ESX server in the same high-availability cluster.

Not all disaster recovery needs involve large data center-wide scenarios. In many cases, the physical hardware on a server can fail, causing critical company applications to be unavailable. VMHA can provide business continuity by quickly restarting VMs that run on a failed ESX server before you are able to get up out of bed and find out why you got a text message about an application outage.

The limits of VMHA

 Even though VMHA makes all your virtual machines high-availability servers, those guest VMs still have to be rebooted after they have moved. And, VMHA works on the assumption that either guest the OS hung or the physical ESX Server crashed.

If you want a technology that doesn't require a VM in the server cluster to be rebooted, check out VMware Fault Tolerance.

VMware's High Availability (VMHA) is offered in 5 of the 6 vSphere Editions - Essentials Plus, Standard, Advanced, Enterprise and Enterprise Plus. Additionally VMware's vCenter is required.

For more information, read VMware's High Availability product page.

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About the author
David Davis is the director of infrastructure at TrainSignal.com -- the global leader in video training for IT pros. He has several certifications including vExpert, VMware Certified Profession (or VCP), CISSP, and CCIE #9369. Additionally, Davis has authored hundreds of articles and six video training courses at Train Signal, where one of the most popular course is the VMware vSphere 4 video training course. His website is VMwareVideos.com. You can follow Davis on Twitter or connect with him at David on LinkedIn.

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