VMware Fault Tolerance (FT) is a new high availability feature in VMware's vSphere 4. With Fault Tolerance, your virtual guest machine runs on a primary ESX host server while the memory of that virutual machine (VM) is mirrored (using vLockstep) over to a secondary (ghost) ESX host server. If the primary ESX Server fails, the virtual machine immediately resumes operation on the secondary ESX Server with zero downtime to the VM, application or end user using that VM.
The benefits of VMware Fault Tolerance
Unlike traditional high-availability (HA) technologies, VMware's Fault Tolerance works regardless of the operating system, and you aren't charged for every server that uses this HA feature. FT is based on VMware Workstation's Record/Replay features that can play back what happened in a VM.
Fault Tolerance is not used for load balancing - it is strictly for high availability of a VM in the event that an ESX Server goes down. Unlike VMware HA clusters (VMHA), with FT, the VM that was protected doesn't have to be rebooted. Thus, with FT, unlike VMHA, there is no downtime for end users.
The best thing about VMware FT is that to enable it, all you need to do is to right-click on the primary VM and enable Fault Tolerance. At that point, FT takes over, creating the secondary VM that will protect the primary VM if the ESX server running the primary VM has a failure.
VMware FT requires Intel 31xx, 33xx, 52xx, 54xx, 55xx, 74xx or AMD 13xx,23xx, 83xx series of processors (or greater). Moreover, you can't run FT on just any vSphere-compatible server because FT uses special features of the CPU. Today, FT is also supported only on VMs that have a single CPU (no multiprocessor VMs can use FT).
High availability, in general, is an excellent part of any large scale disaster recovery strategy. With Fault Tolerance you have the added protection for smaller-scale disasters such as the loss of a single ESX host server running 50+ virtual machines.
VMware's Fault Tolerance (FT) is offered in 3 of the 6 vSphere Editions - Advanced, Enterprise and Enterprise Plus. Additionally, VMware's vCenter is required.
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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 on LinkedIn.
This was first published in November 2009