In a vSAN policy the configuration you will have is Raid 1, Raid 5 and Raid 6. The failure to tolerate (ftt) can be 1, 2 or 3 for a vSAN cluster. Meaning how many hosts in your cluster can tolerate failure before you lose data. The below is a table with those configurations, but if you want to work it out manually this is how you do it.
Raid 1 calculation is 2(n)+1 which is 2 x ftt + 1 = the number of esxi hosts required
Raid 5 & 6 calculation is 2(n)+2 which is 2 x ftt + 2 = the number of esxi hosts required
Example calculation for RAID 1
Raid 1 calculation is, the number of hosts require = 2(n)+1
If you want to tolerate three failed hosts the calculation would be 2 x 3 + 1 = 7
7 is number of esxi hosts you will need in your vSAN cluster
3 is the number of ESXi hosts that can fail in your vSAN cluster
Example calculation for RAID 6
Raid 5 calculation is, the number of hosts required = 2(n)+2
If you want to tolerate two failed hosts the calculation would be 2 x 2 + 2 = 6
6 is number of esxi hosts you will need in your vSAN cluster
2 is the number of ESXi hosts that can fail in your vSAN cluster