Choosing a disk type

Find out how to choose between the VMware disk types

Last updated 2nd February 2022


VMware offers 3 types of disks for virtual machines.

This guide explains the differences between the available disk types.


Thin provision

Thin provisioning means that only the actual size of the disk will be consumed on the datastore. The size will grow along with the content.

For example, a 1TB disk can be allocated that will be recognised as 1TB by the VM operating system, but it will take up only the 20GB of space on the datastore the guest OS occupies.

One could allocate 50 TB (50 1TB VMs allocated) on a 1.2TB datastore, but only occupy 1TB (20GB occupied / VM in our example).

It is important in this situation to control the write consumption of these VMs, so as not to significantly increase the occupancy of the different disks of the VMs and thus fill the datastore.

The full datastore will prevent any new writing and may potentially cause the VMs to stop.

It is not possible to reclaim the occupied space.

Example: If you occupy 40GB on a 100GB thin disk and delete 20GB of data in the VM, the space on the datastore will still be 40GB and the allocated space still 100GB.

Thick Provision Eager Zeroed

This type of disk will occupy all the allocated space on the datastore.

A 100GB thick VM will occupy 100GB of datastore space.

The VM disk is zeroed out (filled with zeros) when the disk is created on the VMFS volume.

Thick Provision Lazy Zeroed

This type of disk will occupy all the allocated space on the datastore.

A 100GB thick VM will occupy 100GB of datastore space.

The allocated space is reserved for the VM disk, but the zeros are written when the VM needs the disk space.


Example summary for 100GB VMs with 40GB guest OS:

Disk type Space allocated Block zeroed Space occupied
Eager Zero At VM creation At VM creation 100GB
Lazy Zero At VM creation When the block is first written 100GB
Thin When the block is first written When the block is first written 40GB

OVHcloud disk types

In a standard storage Hosted Private Cloud infrastructure, only Thin provisioning is possible.

All 3 types of disk are available on vSAN storage.

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