Reclaiming unused VMDK space with storage thin provisioning

Storage thin provisioning can save space on a VMware Virtual Machine Disk File (VMDK), but reclaiming that space requires the use of tools described below.

I have experimented with Virtual Machine Disk Format (VMDK) thin provisioning since the beta release of vSphere 4.0 as I don’t have much storage space to spare.

Before we get into the nuts and bolts of what I discovered, here’s some background on thin provisioning. Normally, when a 50 GB VMDK is created, it immediately eats up 50 GB of disk space on the Virtual Machine File System (VMFS) volume. Since application owners often demand more space than they truly need, there is a lot of expensive storage area network (SAN) disk capacity dedicated to these applications that will never be used. When you thin-provision a VMDK, storage is not allocated to the VMDK unless it is actually used. As long as only 10 GB of the allocated 50 GB disk is used, only 10 GB is claimed.

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