VMware Fault Tolerance is a new feature included in vSphere4 that ensures continuous availability for virtual machines against hardware failures. This feature will allow you to protect any application & any OS without modifications and provides a much more cost-effective way of running mission critical workloads than fault-tolerant hardware dedicated entirely to individual applications. VMware FT creates virtual machine “pairs” or a mirror of VM’s that run in lock step and that are fully redundant instances.
If an unexpected hardware failure occurred on the primary VM, the secondary VM immediately picks up where the primary left off, and continues to run, uninterrupted, and without any loss of network connections or transactions. FT will take advantage of hardware assisted virtualization in CPUs, more and more CPU cores becoming available to offload overhead, and high-speed network improvements like 10gigE to reduce latency.
Limitations of FT initially:
- Dependent on shared storage
- Virtual compatibility mode for RDMs only
- Only thick virtual disks can be used for virtual machine
- Two VMkernel gigabit NICs for FT & Vmotion are required
- Uniprocessor VMs only.
- Additional overhead also associated with this type of solution. Expect more CPU & memory resources will be required to run the 2nd VM, and applications may experience small amounts of added latency.
Referenece Documentation: http://www.vmware.com/pdf/vsphere4/r40/vsp_40_availability.pdf