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VMware Disk Types for Virtual Machines

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VMware offers three kinds of disks for virtual machine. In this article, we will walk through the three different disk types.

Topics

Thin Provision

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

For example, if you allocate a 1 TB disk to a VM but only store 20 GB worth of files on it, the VM will see a 1 TB disk but only 20 GB of datastore storage will actually be used for the VM.

It is possible to allocate 50 TB on a 1.2 TB datastore. However, you could not exceed the maximum 1.2 TB storage on the physical datastore.

Danger

WARNING: In this situation, it is important to control the write consumption of the VMs in question so as not to significantly increase the occupancy of the VM disks, which would cause you to fill the datastore. A full datastore will prevent any new writing and could potentially cause the VMs to stop running.

It is not possible to reclaim the occupied space on a datastore. For instance, if you had 40 GB on a 100 GB thin-provisioned disk and you deleted 20 GB of data from the VM, the datastore would still reflect 40 GB of used storage and you would still have 100 GB allocated to the disk.

Thick Provision Eager Zeroed

This type of disk will occupy all the allocated space on the datastore. That is to say a 100 GB thick VM will occupy 100 GB of datastore space. The VM disk is zeroed out (filled with zeroes) 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. That is to say a 100 GB thick VM will occupy 100 GB of datastore space. The allocated space is reserved for the VM disk, but the zeroes are written when the VM needs the disk space.

OVHcloud Disk Types

On OVHcloud's physical datastore storage, only thin provisioning is available by default. However, if you choose the vSAN option, all three types of disks are possible.

Conclusion

Having read this article, you should be able to identify the three types of disks VMware uses and what each one does.