[Storage Provisioning] vSphere Convert Thick to Thin Disk

If you accidentally created a virtual disk of thick provisioning, but what you really want is to save on storage space. How can you change it into thin provisioning? Keep reading, this article will show you how to convert a thick disk to thin in vSphere.


By Crystal / Updated on March 17, 2023

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Thick vs thin provisioning

Virtual disk is an important part of virtual machine hardware. Just like physical disks, virtual disks store all the data of a virtual machine, yet better, it is transportable.

When creating a new VM on vSphere, you may have noticed that you can specify a provisioning policy for the virtual disk file. The options include:

  • Thick Provision Lazy Zeroed

Creates a virtual disk in a default thick format. Space required for the virtual disk is allocated when the disk is created. Data remaining on the physical device is not erased during creation, but is zeroed out on demand later on first write from the virtual machine. Virtual machines do not read stale data from the physical device.

  • Thick Provision Eager Zeroed

A type of thick virtual disk that supports clustering features such as Fault Tolerance. Space required for the virtual disk is allocated at creation time. In contrast to the thick provision lazy zeroed format, the data remaining on the physical device is zeroed out when the virtual disk is created. It might take longer to create virtual disks in this format than to create other types of disks. Increasing the size of an Eager Zeroed Thick virtual disk causes a significant stun time for the virtual machine.

  • Thin Provision

Use this format to save storage space. For the thin disk, you provision as much datastore space as the disk would require based on the value that you enter for the virtual disk size. However, the thin disk starts small and at first, uses only as much datastore space as the disk needs for its initial operations. If the thin disk needs more space later, it can grow to its maximum capacity and occupy the entire datastore space provisioned to it.

Here is a table showing the difference between thin provision vs thick.

Provision type Thin provisioning Thick provisioning
Total disk size grow as data written fixed
Size at creation smaller larger
Space saving yes no
Creation time shorter longer
Latency more less
Need Monitoring more less

If you wrongly created a thick provisioned disk but still want to save on storage space, you may want to change it to thin provisioning. The next part will show you how to use vSphere convert thick to thin provisioning.

How to convert a thick disk to thin in vSphere

To convert a virtual machine base disk from thick to thin provisioning, you can use the storage vMotion feature provided by vSphere.

Before you start, please make sure that you have a valid backup of the target virtual machine and more than one datastore. If only a single datastore exists, you can clone the virtual machine to a destination machine with thin provisioned disks instead of migrating.

Here are the specific steps:

1. Right-click on the target virtual machine and select Migrate.


2. It will pop up a wizard. On Select a migration type page, select Change storage only option and click Next to continue.

Change storage only

3. On Select storage page, select the option Configure per disk, and then select the target disk that needs to modify.

Configure per disk

4. Under Storage category select the destination datastore and under the Disk Format option select Thin Provision.

Thin provision

5. Validate the required VM Storage Policy and click Next.

6. Review the information on the Review Selections page and click Finish.

Backup to protect VM data stored on your virtual disks

You may need a reliable backup software to protect the virtual disks of your vSphere VMs, and gain the ability to quickly recover your virtual machines when needed.

You can try the reliable and efficient vSphere backup software - AOMEI Cyber Backup. It simplifies the backup process and present the steps with intuitive GUI interface. In addition, it offers you the following benefits.

Agentless Backup: create complete and independent image-level backup for VMware ESXi and Hyper-V VMs.
Flexible vSphere Backup: batch backup large numbers of VMs managed by vCenter Server, or multiple VMs on a standalone ESXi host.
Multiple Storage Destinations: backup to local drive, or network destinations like Windows share or NAS.
Automated Execution: create backup schedules to automate backups daily, weekly, monthly.
Role Assignment: allows one administrator to create sub-accounts with limited privileges.

AOMEI Cyber Backup supports both paid and free versions of VMware ESXi 6.0 and later versions. Next, I will show you how to perform vSphere VM backup and restore via AOMEI Cyber Backup. You can click the following button to download the 30-day free trial.

Download Free TrialVMware ESXi & Hyper-V
Secure Download

*You can choose to install this VM backup software on either Windows or Linux system.

Steps to perform vSphere backup and restore via AOMEI Cyber Backup

Backup multiple VMs:

1. Bind Devices: Access to AOMEI Cyber Backup web client, navigate to Source Device > VMware > + Add VMware Device to Add vCenter or Standalone ESXi host. And then click > Bind Device.

Add VMware ESXi host

2. Create Backup Task: Navigate to Backup Task > + Create New Task, and select VMware ESXi Backup as the Backup Type.

3. Set the Task Name, Device, Target, Schedule and Cleanup as needed.

  • Task Name: you can change the task name or use the default name with an ordinal.
  • Device: batch backup multiple VMs (10 on free edition) on vCenter or standalone host within one backup task.
  • Target: select to back up to a local path, or to a network path like NAS.
  • Schedule (optional): perform full, differential, or incremental backup, and automate execution according to the frequency you specified.
  • Cleanup (optional): automatically delete the old backup copies that exceed the retention period you specified.

4. Run Backup: Now you can click Start Backup and select Add the schedule and start backup now, or Add the schedule only.

Start Backup

Created backup tasks will be listed and monitored separately for restoring, progress checking and schedule changing.

Restore VM from backup:

5. Restore from Backup: Select the backup task you want to restore, and click ... > Restore to open the wizard.

Or you can click Backup Management > History Versions. Specify a VM and select a restore point from the left list.

6. Start Restore: Choose to Restore to original location or Restore to new location. And click Start Restore to recover the virtual machine in place.

Restore to new location: Create a new VM in the same or another datastore/host directly from the backup to perform out-of-spacre recovery, saves the trouble of re-configuring the new VM.

Restore to new location


vSphere provides different disk provisioning policies for users to customize according to their own needs. This article introduced what’s thick and thin provisioning, and showed how to convert a thick disk to thin in vSphere using vMotion.

In order not to lose data for accidental errors, please remember to backup your vSphere VMs before you start using vSphere convert thick to thin provisioning.

Crystal · Editor
Crystal is an editor from AOMEI Technology. She mainly writes articles about virtual machine. She is a positive young lady likes to share articles with peolpe. Off work she loves travelling and cooking which is wonderful for life.