The best sizing tool for VSAN:

Quote from the site:

The purpose of this tool is to help determine the hardware specifications for hosts in a Virtual SAN cluster required to run a set of virtual machines defined by a set of input characteristics. These important assumptions should be understood before using this tool:

  • All hosts in the cluster are assumed to have an identical hardware profile, i.e. numbers of hard drives and flash devices, amount of physical RAM, and number of CPU cores
  • All virtual machines are assumed to be identical in storage characteristics, i.e. number of VMDKs, size of VMDKs (assumed identical for all disks), number of snapshots, and virtual memory size
  • All virtual machines are assumed to have the same Virtual SAN policy, i.e. number of failures to tolerate and number of disk stripes per object
  • The tool is designed so that you can easily vary inputs to see the impact on the sizing output, thus allowing you to iterate manually for more sophisticated analyses.

So now the question is how does it work???

Calculation of IOPS is a VSAN cluster is one of the most asked questions.O n the calculator, You can input how many VMs in the cluster, average VMs/Host, and some parameters for per-VM profiling. Then, it can tell you how many IOPS your cluster needs.

For Server Virtualization:

Total IOPS Required for Cluster = #VMs * (1.3 * IOPS/VM – 100 * %Read + 70)

For Desktop Virtualization:

Total IOPS Required for Cluster = #VMs * (1.7 * IOPS/VM – 25 * %Read + 7.5)

Please follow the VSAN guide for further reference: