2.2.3 Failures to Tolerate policy
The failures to tolerate virtual machine policy (FTT or NumberOfFailuresToTolerate) regulates the number of failures the vSAN underlying the VM is able to sustain while the VM remains available. The fault domains and the FTT policy are tightly related when both are configured.
The following table reports the FTT values with the associated number of fault domains to implement to support the policy, and the common formula to calculate the fault domains (2n+1) when the FTT value (n) is selected.
Table 1. FTT Policy and Required Hosts
Number of Failures To Tolerate (FTT) | Number of Fault Domains Required |
n | 2n + 1 |
1 | 3 |
2 | 5 |
3 (maximum) | 7 |
The more virtual machines that are deployed with the FTT policy enabled and the higher the value of the policy setting, the greater the impact on the storage capacity requirements for the vSAN environment.
1 Virtual SAN 6.2 RAID Fault Tolerance methods require additional considerations.