VMware ESXi and vSphere Cluster Management

Inflate a Thin-Provisioned Virtual Disk to Thick Provisioning in VMware ESXi

Learn how to convert an existing thin-provisioned VMware VMDK to thick provisioning with the vSphere datastore browser, including prechecks, inflation steps, validation, and troubleshooting.

Overview

VMware administrators can use the Inflate action to convert an existing thin-provisioned virtual disk into a thick-provisioned disk. The operation allocates the disk's remaining capacity on its datastore, but it does not make the disk larger from the guest operating system's perspective.

This procedure uses the vSphere client and datastore browser. Before starting, identify the correct virtual machine, datastore, and VMDK. A VMDK is the VMware virtual machine disk file that represents a virtual disk.

Thin and thick virtual disk provisioning

Thin provisioning allocates datastore space as virtual disk blocks are written. A thin disk can have a large configured capacity while initially consuming much less physical capacity on the datastore.

Thick provisioning allocates the disk's configured capacity on the datastore. The datastore therefore reserves or consumes space for the full virtual disk capacity, subject to the specific thick-disk format and storage implementation.

Two capacities must be kept separate:

Virtual disk capacity: the maximum size presented to the guest operating system, such as 10 GB or 500 GB.
Physical datastore consumption: the amount of storage currently occupied by the VMDK and related files on the datastore.

Characteristic	Thin-Provisioned Disk	Thick Disk After Inflation
Initial datastore consumption	Usually less than the configured capacity; usage reflects blocks already allocated or written.	Near the configured capacity is allocated on the datastore.
Growth of physical usage	Datastore usage grows as additional virtual disk blocks are written.	Additional growth from ordinary writes is generally avoided because the disk capacity has already been allocated.
Configured guest-visible capacity	Unchanged; the guest sees the full configured virtual disk size.	Unchanged; inflation does not increase the virtual disk size.
Datastore capacity-planning implications	Requires monitoring so aggregate thin-disk growth does not exhaust the datastore.	Requires capacity for the full disk size up front, plus operational headroom.
Result of the Inflate operation	The remaining unallocated capacity is allocated.	The VMDK becomes thick-provisioned.

What disk inflation does

Inflate is the operation that allocates the remaining datastore blocks for an existing thin VMDK until its full configured capacity is consumed. It changes the disk from thin provisioning to a thick format.

For example, suppose a virtual machine has a 10 GB thin VMDK and the datastore currently reports about 3 GB of consumption for that disk. Inflation allocates roughly the remaining 7 GB, so datastore usage becomes near 10 GB. The guest continues to see a 10 GB disk, and its existing data remains in place.

Inflation is not the same as virtual disk expansion. It does not:

Increase the virtual disk's configured capacity.
Expand a partition inside Windows or Linux.
Extend a filesystem.
Give the guest additional usable space.

If the guest must see a larger disk, use a separate virtual-disk expansion procedure and then extend the guest partition and filesystem as appropriate.

Pre-inflation planning and checks

Complete the following checks before opening the Inflate action.

Check	Why It Matters	How to Verify
Virtual machine powered off	The guest should be shut down before changing disk provisioning, reducing the risk of active I/O or an unavailable action.	Shut down the guest operating system cleanly, then confirm that the vSphere inventory shows the virtual machine as powered off.
Correct datastore identified	The operation requires enough free capacity on the datastore that holds the target VMDK.	Review the virtual machine's storage configuration and locate its files in the appropriate datastore.
Correct VMDK identified	A virtual machine may contain separate operating-system and data disks. Selecting the wrong file can affect the wrong disk or fail to perform the intended task.	Cross-reference the virtual machine hardware settings with the datastore directory, file names, and sizes.
Sufficient datastore free space	Inflation needs space for the disk's unallocated remainder and should not consume all operational capacity.	Compare the disk's configured capacity with its current consumption, then check datastore free space and maintain reasonable headroom.
Snapshot status reviewed	A snapshot can create dependent delta disks and a disk chain. Changing the wrong file in a chain can produce an invalid or unintended result.	Review the virtual machine's snapshot manager and identify whether snapshot-related files are present before acting.
Backup or recovery plan available	A storage-format change should be recoverable if the task fails or an unexpected issue occurs.	Confirm a recent usable backup, replication copy, or other tested recovery method.

Calculate the required additional capacity

Estimate the space required using:

additional capacity ≈ configured virtual disk capacity − current datastore consumption

For a 500 GB thin disk consuming 120 GB, plan for approximately 380 GB of additional datastore capacity. Do not plan for only the exact calculated remainder: other virtual machines, temporary files, snapshots, metadata, and concurrent storage activity require additional headroom.

Inflate the VMDK with the vSphere client

Identify the target disk. In the virtual machine's hardware or storage settings, determine whether the target is the operating-system disk or a data disk. Record its datastore and file location.
Shut down the guest operating system. Use the normal shutdown process inside the guest whenever possible.
Verify power state. In the vSphere client, confirm that the virtual machine is powered off before changing the disk.
Open the datastore browser. Navigate to the datastore that contains the target VMDK and open its file browser.
Open the virtual machine directory. Locate the folder associated with the virtual machine and review its files.
Select the intended VMDK. Cross-check the file name and size against the virtual machine hardware configuration. Avoid selecting unrelated files, configuration files, logs, or snapshot delta files.
Open the context menu. Right-click the target VMDK and choose Inflate. Interface labels and menu placement can vary among vSphere and ESXi versions.
Monitor the task. Watch Recent Tasks or the task pane until the operation reports successful completion. Do not interrupt the operation or power on the virtual machine while it is running.
Power on the virtual machine. After successful completion, start the virtual machine and check its normal boot process.

Post-conversion validation

Check the datastore summary or browser and confirm that physical consumption increased to near the disk's full configured capacity.
Confirm that the virtual machine starts normally.
Inside the guest, verify that the same disk size is visible as before. Inflation should not change the guest-visible capacity.
Confirm that expected files, applications, and data are available.
Review Recent Tasks, events, and alarms for errors or warnings related to the datastore or virtual machine.
Continue monitoring datastore free space after the conversion, especially when multiple thin disks share the datastore.

Troubleshooting

The Inflate action is unavailable

Common causes include selecting the wrong file type, leaving the virtual machine powered on, lacking the required permissions, or using a vSphere or ESXi version with a different workflow.

Confirm that the selected item is the intended VMDK.
Power off the virtual machine cleanly and verify its power state.
Check the administrator's virtual machine and datastore permissions.
Use the datastore-browser workflow applicable to the installed vSphere version.

The task fails because of insufficient space

The datastore may not have enough capacity for the thin disk's remaining unallocated space. Other workloads or temporary storage requirements may also reduce available capacity while the task is running.

Recalculate the expected additional allocation.
Free capacity or move workloads to another datastore.
Retry only after confirming sufficient space and reasonable free-space headroom.

The guest partition did not become larger

This is expected. Inflation changes datastore allocation, not the configured virtual disk size. To provide more guest space, expand the virtual disk separately and then extend the guest partition and filesystem.

The target disk is difficult to identify

Multiple VMDKs, non-obvious file names, and snapshot-related files can make selection difficult. Cross-reference the virtual machine hardware settings with datastore file names and sizes. Review snapshot status before acting on any disk chain, and do not select a file merely because it appears in the same directory.

Operational cautions

Inflation can require a large amount of free datastore capacity and may fail if capacity becomes insufficient.
The operation targets a VMDK, so selecting an unrelated file can produce an error or an unintended result.
Interface labels, permissions, and available actions differ among vSphere and ESXi releases.
Snapshot disk chains require extra care. Identify the active disk chain and follow your organization's snapshot-management procedure before changing provisioning.
Convert a disk to thick provisioning for a documented storage, performance, capacity-planning, or policy requirement. Thick provisioning is not universally necessary or automatically better for every workload.

Key points

Thin provisioning separates guest-visible capacity from current datastore consumption.
Inflate allocates the remaining capacity of a thin VMDK and converts it to thick provisioning.
The guest sees the same disk size and data after inflation.
Estimate the unallocated remainder and preserve datastore headroom before starting.
Shut down the virtual machine, select the correct VMDK, monitor the task, and validate the result afterward.

For related storage administration procedures, see Inflate Thin Disk.