FT Information

http://www.vmware.com/products/fault-tolerance/
Meet the Engineer Series: VMware Fault Tolerance
http://tech.philipsellers.com/2008/09/20/introduction-to-vmware-ft-fault-tolerence/
http://kb.vmware.com/kb/1010601 - Understanding VMware Fault Tolerance
http://kb.vmware.com/kb/1013428 - VMware Fault Tolerance FAQ
FT not supported on Nehalem systems with hyperthreading enabled?

About vLockStep:
http://software.intel.com/en-us/blogs/2009/05/28/instruction-level-lock-step-parallelism-on-desert-islands/
http://mordtech.com/tag/vlockstep/

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FT requirements

http://kb.vmware.com/kb/1008027 - Processors and guest operating systems that support VMware Fault Tolerance

To check compatibility there is also a VMware utility:
Site Survey - http://www.vmware.com/download/shared_utilities.html

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FT 1.0 limitations

• Only 1 vCPU for each VM protected by FT
• Require compatible CPU (http://kb.vmware.com/kb/1008027)
• No vmxnet3 support (http://kb.vmware.com/kb/1013757)
• No snapshot support (and no VCB and other snap-based backup program)
• No physical RDM (Need clearification on FT requirement)
• Do not use both ESX and ESXi hosts in clusters with fault tolerant virtual machines (http://kb.vmware.com/kb/1013637)

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FT vs VM HA or MSCS

FT does not protect against OS or application failures, only ESX host failures.
Clarificaiton on Fault Tolerance

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Enable/Disable FT with script

Could be useful to implement some backup solution on FT protected VM.
on-demand FT, can this be automated?
ftCLI.pl - VMware Fault Tolerant Managment