VMware Datastore Capacity Calculator

space per VM = consumed VMDK + (configured RAM × (1 − reservation)) for the swap file + snapshot allowance; VMs supported = raw size × (1 − free reserve) ÷ space per VM. A VM costs a datastore more than its VMDK. Every powered-on VM without a full memory reservation also writes a .vswp file the size of its configured RAM, snapshots grow delta disks that can rival the base disk, and thin provisioning only defers the VMDK cost rather than removing it. Subtracting a free reserve first is what keeps the datastore operable rather than merely full.

A datastore at 95% cannot consolidate a snapshot or accept a Storage vMotion, so it fails exactly when you need the tools that would rescue it — and thin provisioning means the wall arrives without warning.

This calculator takes 9 inputs: Datastore raw size, VMs on this datastore, Provisioned disk per VM, Actual disk consumed, Thin provisioning enabled, Configured memory per VM, Memory reserved per VM, Snapshot delta allowance, Free space kept in reserve. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

Yes. The .vswp file is sized as configured RAM minus the reservation, so a 100% reservation creates no swap file at all. That trades datastore space for a permanent claim on host memory, which lowers the memory overcommit you can run.