Fault Tolerance

Fault Tolerance (FT) is a feature of vSphere HA cluster. Hence to be able to use FT you need to configure an HA cluster first. FT is enabled on those VMs which need a higher level of protection. On enabling FT on the selected VM, a selected VM becomes primary and a new secondary VM is created on one of the hosts in the HA cluster.

Requirements for enabling FT on VMs:

  • HA Cluster should be configured for EVC
  • Configure a VMKernel portgroup enabled for FT Logging on all ESXi hosts (part of a HA Cluster) which would host FT VMs
  • Virtual disks on FT VMs have to be “Thick Provisioned Eager Zeroed”
  • ISO/Floppy images have to be stored on Shared Storage
  • Hosts in cluster Should meet vMotion requirements
    • Shared Storage
    • vMotion Portgroup
    • Visibility to same Physical Networks
    • Compatible Processors
  • Both FT VMs (Primary & Secondary) would be configured with full reservation for CPU & Memory

FAQs on FT VMs:

Q. Does FT support vSMP on VMs?
A. No. VMs with vSMP cannot be enabled for FT. i.e. VMs with more than 1 vCPU cannot be protected with FT.

Q. Is FT supported on AMD processors.
A. Yes, both Intel & AMD processors are supported for FT. The VMware’s KB#1008027 article lists what processors and guest operating systems are supported for FT.

Q. How many FT VMs can be hosted on a single ESXi host?
A. Maximum 4 FT VMs supported per ESXi host (either Primaries or Secondaries).

Q. What is a primary VM?
A. Primary VM is a VM which is serving the user requests. The access to this VM is always read-write.

Q. What is a secondary VM?
A. Secondary is a backup VM, which is promoted to primary in case of (original) Primary VM failure. When it is a Secondary VM, the access to this VM is always read-only.


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