How to convert VMware virtual disks from thin to thick with the vSphere client

Posted February 2, 2011 by Ben in Networking

Have you ever provisioned a new virtual machine in vSphere, put it in production, and discovered belatedly that you mistakenly used “thin provisioned” virtual disks? This can often happen when deploying from a template which was thin provisioned since the default option is to use the same disk format as the source. Good news! It is quite easy to convert these to thick with the vSphere client and your mouse.

No command line required, as was the case with previous versions of VMware Infrastructure. The only downside is that the virtual machine must be shut down prior to inflating its disk(s).

1. Launch your vSphere client and log in to your vCenter server.

2. Select the virtual machine which has mistakenly been thin provisioned.

3. Select the option to “Shut Down Guest” under Commands. This is a necessary step. If your virtual machine is in production, you will have to schedule some downtime.

4. Right-click the virtual machine and select the Snapshot menu. If you see the option to “Revert to snapshot”, it means that you have at least one snapshot of this virtual machine. I highly recommend that you remove all snapshots by opening Snapshot Manager and selecting Delete All. Please keep in mind that this has its own implications so please understand them before continuing.

4. Look at the Datastore list on the right to see what Datastores your virtual machine is using. Note the free space listed – you must have enough free space to allow the disks to expand to their “provisioned” size or you will cause yourself quite a headache!

5. Now right-click the Datastore and select “Browse Datastore…”

6. Select the folder for your virtual machine on the left, and the contents will show on the right.

7. Look for the file(s) ending in the “.vmdk” extension. These will be labeled “Virtual Disk” under the “Type” header. Note the “Provisioned Size” header and make sure that you have enough free space in this datastore to support your virtual disk(s) growing to consume this space.

8. Finally, to inflate your virtual machine’s disk you simply right-click the .vmdk and select “Inflate”. Depending on the size of the disk and your underlying storage architecture, this may take quite some time.

9. If the virtual machine has more than one virtual disk that needs to be inflated simply repeat step 8.

10. When complete, the inflated virtual disk will be “eager zeroed thick”, which is the highest performing type of virtual disk in vSphere land.

The Conversation

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  • Cragdoo

    there is an easier way , without downtime to the VM. Migrate the VM to a different datastore , and part of the migration process asks you if want to keep the disk format same as source (in this case think) or convert to thin ..et voila no downtime

  • Ben Kendall

    Thank you for the comment, Cragdoo! Indeed, you are correct, but it can often be the case that there is not another datastore available to migrate to (or your SAN team just won’t give you one). Also, not everyone owns the necessary licenses to use “Storage vMotion”, which is what you’re describing. If you have the storage and the licenses, you are absolutely right that Storage vMotion is the way to go.

  • mark conger

    Nice article and a great tip. I was hoping that there would be a note about how to go from thick to thin to fully round out the content. Sure, there are ways to do it without using a VMware utility but I’m always looking for something faster and easier – and supported!